diff --git a/src/OpenTelemetry.Exporter.Zipkin/.publicApi/PublicAPI.Shipped.txt b/src/OpenTelemetry.Exporter.Zipkin/.publicApi/PublicAPI.Shipped.txt
index 5d94b912d2d..2e1bf086dc7 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/.publicApi/PublicAPI.Shipped.txt
+++ b/src/OpenTelemetry.Exporter.Zipkin/.publicApi/PublicAPI.Shipped.txt
@@ -1,13 +1,14 @@
+#nullable enable
 OpenTelemetry.Exporter.ZipkinExporter
-OpenTelemetry.Exporter.ZipkinExporter.ZipkinExporter(OpenTelemetry.Exporter.ZipkinExporterOptions options, System.Net.Http.HttpClient client = null) -> void
+OpenTelemetry.Exporter.ZipkinExporter.ZipkinExporter(OpenTelemetry.Exporter.ZipkinExporterOptions! options, System.Net.Http.HttpClient? client = null) -> void
 OpenTelemetry.Exporter.ZipkinExporterOptions
-OpenTelemetry.Exporter.ZipkinExporterOptions.BatchExportProcessorOptions.get -> OpenTelemetry.BatchExportProcessorOptions<System.Diagnostics.Activity>
 OpenTelemetry.Exporter.ZipkinExporterOptions.BatchExportProcessorOptions.set -> void
-OpenTelemetry.Exporter.ZipkinExporterOptions.Endpoint.get -> System.Uri
+OpenTelemetry.Exporter.ZipkinExporterOptions.BatchExportProcessorOptions.get -> OpenTelemetry.BatchExportProcessorOptions<System.Diagnostics.Activity!>!
+OpenTelemetry.Exporter.ZipkinExporterOptions.HttpClientFactory.get -> System.Func<System.Net.Http.HttpClient!>!
+OpenTelemetry.Exporter.ZipkinExporterOptions.Endpoint.get -> System.Uri!
 OpenTelemetry.Exporter.ZipkinExporterOptions.Endpoint.set -> void
 OpenTelemetry.Exporter.ZipkinExporterOptions.ExportProcessorType.get -> OpenTelemetry.ExportProcessorType
 OpenTelemetry.Exporter.ZipkinExporterOptions.ExportProcessorType.set -> void
-OpenTelemetry.Exporter.ZipkinExporterOptions.HttpClientFactory.get -> System.Func<System.Net.Http.HttpClient>
 OpenTelemetry.Exporter.ZipkinExporterOptions.HttpClientFactory.set -> void
 OpenTelemetry.Exporter.ZipkinExporterOptions.MaxPayloadSizeInBytes.get -> int?
 OpenTelemetry.Exporter.ZipkinExporterOptions.MaxPayloadSizeInBytes.set -> void
@@ -15,7 +16,7 @@ OpenTelemetry.Exporter.ZipkinExporterOptions.UseShortTraceIds.get -> bool
 OpenTelemetry.Exporter.ZipkinExporterOptions.UseShortTraceIds.set -> void
 OpenTelemetry.Exporter.ZipkinExporterOptions.ZipkinExporterOptions() -> void
 OpenTelemetry.Trace.ZipkinExporterHelperExtensions
-override OpenTelemetry.Exporter.ZipkinExporter.Export(in OpenTelemetry.Batch<System.Diagnostics.Activity> batch) -> OpenTelemetry.ExportResult
-static OpenTelemetry.Trace.ZipkinExporterHelperExtensions.AddZipkinExporter(this OpenTelemetry.Trace.TracerProviderBuilder builder, string name, System.Action<OpenTelemetry.Exporter.ZipkinExporterOptions> configure) -> OpenTelemetry.Trace.TracerProviderBuilder
-static OpenTelemetry.Trace.ZipkinExporterHelperExtensions.AddZipkinExporter(this OpenTelemetry.Trace.TracerProviderBuilder builder, System.Action<OpenTelemetry.Exporter.ZipkinExporterOptions> configure) -> OpenTelemetry.Trace.TracerProviderBuilder
-static OpenTelemetry.Trace.ZipkinExporterHelperExtensions.AddZipkinExporter(this OpenTelemetry.Trace.TracerProviderBuilder builder) -> OpenTelemetry.Trace.TracerProviderBuilder
+override OpenTelemetry.Exporter.ZipkinExporter.Export(in OpenTelemetry.Batch<System.Diagnostics.Activity!> batch) -> OpenTelemetry.ExportResult
+static OpenTelemetry.Trace.ZipkinExporterHelperExtensions.AddZipkinExporter(this OpenTelemetry.Trace.TracerProviderBuilder! builder) -> OpenTelemetry.Trace.TracerProviderBuilder!
+static OpenTelemetry.Trace.ZipkinExporterHelperExtensions.AddZipkinExporter(this OpenTelemetry.Trace.TracerProviderBuilder! builder, string? name, System.Action<OpenTelemetry.Exporter.ZipkinExporterOptions!>? configure) -> OpenTelemetry.Trace.TracerProviderBuilder!
+static OpenTelemetry.Trace.ZipkinExporterHelperExtensions.AddZipkinExporter(this OpenTelemetry.Trace.TracerProviderBuilder! builder, System.Action<OpenTelemetry.Exporter.ZipkinExporterOptions!>! configure) -> OpenTelemetry.Trace.TracerProviderBuilder!
diff --git a/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinActivityConversionExtensions.cs b/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinActivityConversionExtensions.cs
index 802591d052a..2753f51f50a 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinActivityConversionExtensions.cs
+++ b/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinActivityConversionExtensions.cs
@@ -21,13 +21,13 @@ internal static ZipkinSpan ToZipkinSpan(this Activity activity, ZipkinEndpoint l
     {
         var context = activity.Context;
 
-        string parentId = activity.ParentSpanId == default ?
+        string? parentId = activity.ParentSpanId == default ?
             null
             : EncodeSpanId(activity.ParentSpanId);
 
         var tagState = new TagEnumerationState
         {
-            Tags = PooledList<KeyValuePair<string, object>>.Create(),
+            Tags = PooledList<KeyValuePair<string, object?>>.Create(),
         };
 
         tagState.EnumerateTags(activity);
@@ -38,9 +38,9 @@ internal static ZipkinSpan ToZipkinSpan(this Activity activity, ZipkinEndpoint l
         {
             if (activity.Status == ActivityStatusCode.Ok)
             {
-                PooledList<KeyValuePair<string, object>>.Add(
+                PooledList<KeyValuePair<string, object?>>.Add(
                 ref tagState.Tags,
-                new KeyValuePair<string, object>(
+                new KeyValuePair<string, object?>(
                     SpanAttributeConstants.StatusCodeKey,
                     "OK"));
             }
@@ -48,16 +48,16 @@ internal static ZipkinSpan ToZipkinSpan(this Activity activity, ZipkinEndpoint l
             // activity.Status is Error
             else
             {
-                PooledList<KeyValuePair<string, object>>.Add(
+                PooledList<KeyValuePair<string, object?>>.Add(
                     ref tagState.Tags,
-                    new KeyValuePair<string, object>(
+                    new KeyValuePair<string, object?>(
                         SpanAttributeConstants.StatusCodeKey,
                         "ERROR"));
 
                 // Error flag rule from https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md#status
-                PooledList<KeyValuePair<string, object>>.Add(
+                PooledList<KeyValuePair<string, object?>>.Add(
                     ref tagState.Tags,
-                    new KeyValuePair<string, object>(
+                    new KeyValuePair<string, object?>(
                         ZipkinErrorFlagTagName,
                         activity.StatusDescription ?? string.Empty));
             }
@@ -67,18 +67,18 @@ internal static ZipkinSpan ToZipkinSpan(this Activity activity, ZipkinEndpoint l
         // activity status takes precedence over status tag.
         else if (tagState.StatusCode.HasValue && tagState.StatusCode != StatusCode.Unset)
         {
-            PooledList<KeyValuePair<string, object>>.Add(
+            PooledList<KeyValuePair<string, object?>>.Add(
                 ref tagState.Tags,
-                new KeyValuePair<string, object>(
+                new KeyValuePair<string, object?>(
                     SpanAttributeConstants.StatusCodeKey,
                     StatusHelper.GetTagValueForStatusCode(tagState.StatusCode.Value)));
 
             // Error flag rule from https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md#status
             if (tagState.StatusCode == StatusCode.Error)
             {
-                PooledList<KeyValuePair<string, object>>.Add(
+                PooledList<KeyValuePair<string, object?>>.Add(
                     ref tagState.Tags,
-                    new KeyValuePair<string, object>(
+                    new KeyValuePair<string, object?>(
                         ZipkinErrorFlagTagName,
                         tagState.StatusDescription ?? string.Empty));
             }
@@ -87,30 +87,30 @@ internal static ZipkinSpan ToZipkinSpan(this Activity activity, ZipkinEndpoint l
         var activitySource = activity.Source;
         if (!string.IsNullOrEmpty(activitySource.Name))
         {
-            PooledList<KeyValuePair<string, object>>.Add(ref tagState.Tags, new KeyValuePair<string, object>("otel.scope.name", activitySource.Name));
+            PooledList<KeyValuePair<string, object?>>.Add(ref tagState.Tags, new KeyValuePair<string, object?>("otel.scope.name", activitySource.Name));
 
             // otel.library.name is deprecated, but has to be propagated according to https://github.com/open-telemetry/opentelemetry-specification/blob/v1.31.0/specification/common/mapping-to-non-otlp.md#instrumentationscope
-            PooledList<KeyValuePair<string, object>>.Add(ref tagState.Tags, new KeyValuePair<string, object>("otel.library.name", activitySource.Name));
+            PooledList<KeyValuePair<string, object?>>.Add(ref tagState.Tags, new KeyValuePair<string, object?>("otel.library.name", activitySource.Name));
             if (!string.IsNullOrEmpty(activitySource.Version))
             {
-                PooledList<KeyValuePair<string, object>>.Add(ref tagState.Tags, new KeyValuePair<string, object>("otel.scope.version", activitySource.Version));
+                PooledList<KeyValuePair<string, object?>>.Add(ref tagState.Tags, new KeyValuePair<string, object?>("otel.scope.version", activitySource.Version));
 
                 // otel.library.version is deprecated, but has to be propagated according to https://github.com/open-telemetry/opentelemetry-specification/blob/v1.31.0/specification/common/mapping-to-non-otlp.md#instrumentationscope
-                PooledList<KeyValuePair<string, object>>.Add(ref tagState.Tags, new KeyValuePair<string, object>("otel.library.version", activitySource.Version));
+                PooledList<KeyValuePair<string, object?>>.Add(ref tagState.Tags, new KeyValuePair<string, object?>("otel.library.version", activitySource.Version));
             }
         }
 
-        ZipkinEndpoint remoteEndpoint = null;
+        ZipkinEndpoint? remoteEndpoint = null;
         if (activity.Kind == ActivityKind.Client || activity.Kind == ActivityKind.Producer)
         {
-            PeerServiceResolver.Resolve(ref tagState, out string peerServiceName, out bool addAsTag);
+            PeerServiceResolver.Resolve(ref tagState, out string? peerServiceName, out bool addAsTag);
 
             if (peerServiceName != null)
             {
                 remoteEndpoint = RemoteEndpointCache.GetOrAdd((peerServiceName, default), ZipkinEndpoint.Create);
                 if (addAsTag)
                 {
-                    PooledList<KeyValuePair<string, object>>.Add(ref tagState.Tags, new KeyValuePair<string, object>(SemanticConventions.AttributePeerService, peerServiceName));
+                    PooledList<KeyValuePair<string, object?>>.Add(ref tagState.Tags, new KeyValuePair<string, object?>(SemanticConventions.AttributePeerService, peerServiceName));
                 }
             }
         }
@@ -172,7 +172,7 @@ private static string EncodeTraceId(ActivityTraceId traceId, bool useShortTraceI
         return id;
     }
 
-    private static string ToActivityKind(Activity activity)
+    private static string? ToActivityKind(Activity activity)
     {
         return activity.Kind switch
         {
@@ -186,15 +186,15 @@ private static string ToActivityKind(Activity activity)
 
     internal struct TagEnumerationState : PeerServiceResolver.IPeerServiceState
     {
-        public PooledList<KeyValuePair<string, object>> Tags;
+        public PooledList<KeyValuePair<string, object?>> Tags;
 
-        public string PeerService { get; set; }
+        public string? PeerService { get; set; }
 
         public int? PeerServicePriority { get; set; }
 
-        public string HostName { get; set; }
+        public string? HostName { get; set; }
 
-        public string IpAddress { get; set; }
+        public string? IpAddress { get; set; }
 
         public long Port { get; set; }
 
@@ -239,7 +239,7 @@ public void EnumerateTags(Activity activity)
                     PeerServiceResolver.InspectTag(ref this, key, intVal);
                 }
 
-                PooledList<KeyValuePair<string, object>>.Add(ref this.Tags, tag);
+                PooledList<KeyValuePair<string, object?>>.Add(ref this.Tags, tag);
             }
         }
     }
diff --git a/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinEndpoint.cs b/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinEndpoint.cs
index c6c9908b38e..cec7cc7156c 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinEndpoint.cs
+++ b/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinEndpoint.cs
@@ -13,11 +13,11 @@ public ZipkinEndpoint(string serviceName)
     }
 
     public ZipkinEndpoint(
-        string serviceName,
-        string ipv4,
-        string ipv6,
+        string? serviceName,
+        string? ipv4,
+        string? ipv6,
         int? port,
-        Dictionary<string, object> tags)
+        Dictionary<string, object>? tags)
     {
         this.ServiceName = serviceName;
         this.Ipv4 = ipv4;
@@ -26,15 +26,15 @@ public ZipkinEndpoint(
         this.Tags = tags;
     }
 
-    public string ServiceName { get; }
+    public string? ServiceName { get; }
 
-    public string Ipv4 { get; }
+    public string? Ipv4 { get; }
 
-    public string Ipv6 { get; }
+    public string? Ipv6 { get; }
 
     public int? Port { get; }
 
-    public Dictionary<string, object> Tags { get; }
+    public Dictionary<string, object>? Tags { get; }
 
     public static ZipkinEndpoint Create(string serviceName)
     {
diff --git a/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinSpan.cs b/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinSpan.cs
index 8038492a0be..a6ea86f6cea 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinSpan.cs
+++ b/src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinSpan.cs
@@ -11,16 +11,16 @@ internal readonly struct ZipkinSpan
 {
     public ZipkinSpan(
         string traceId,
-        string parentId,
+        string? parentId,
         string id,
-        string kind,
+        string? kind,
         string name,
         long? timestamp,
         long? duration,
         ZipkinEndpoint localEndpoint,
-        ZipkinEndpoint remoteEndpoint,
+        ZipkinEndpoint? remoteEndpoint,
         in PooledList<ZipkinAnnotation> annotations,
-        in PooledList<KeyValuePair<string, object>> tags,
+        in PooledList<KeyValuePair<string, object?>> tags,
         bool? debug,
         bool? shared)
     {
@@ -44,11 +44,11 @@ public ZipkinSpan(
 
     public string TraceId { get; }
 
-    public string ParentId { get; }
+    public string? ParentId { get; }
 
     public string Id { get; }
 
-    public string Kind { get; }
+    public string? Kind { get; }
 
     public string Name { get; }
 
@@ -58,11 +58,11 @@ public ZipkinSpan(
 
     public ZipkinEndpoint LocalEndpoint { get; }
 
-    public ZipkinEndpoint RemoteEndpoint { get; }
+    public ZipkinEndpoint? RemoteEndpoint { get; }
 
     public PooledList<ZipkinAnnotation> Annotations { get; }
 
-    public PooledList<KeyValuePair<string, object>> Tags { get; }
+    public PooledList<KeyValuePair<string, object?>> Tags { get; }
 
     public bool? Debug { get; }
 
@@ -148,7 +148,7 @@ public void Write(Utf8JsonWriter writer)
             writer.WriteEndArray();
         }
 
-        if (!this.Tags.IsEmpty || this.LocalEndpoint.Tags != null)
+        if (!this.Tags.IsEmpty || this.LocalEndpoint!.Tags != null)
         {
             writer.WritePropertyName(ZipkinSpanJsonHelper.TagsPropertyName);
             writer.WriteStartObject();
@@ -161,7 +161,7 @@ public void Write(Utf8JsonWriter writer)
 
             try
             {
-                foreach (var tag in this.LocalEndpoint.Tags ?? Enumerable.Empty<KeyValuePair<string, object>>())
+                foreach (var tag in this.LocalEndpoint!.Tags! ?? Enumerable.Empty<KeyValuePair<string, object?>>())
                 {
                     ZipkinTagWriter.Instance.TryWriteTag(ref writer, tag);
                 }
diff --git a/src/OpenTelemetry.Exporter.Zipkin/OpenTelemetry.Exporter.Zipkin.csproj b/src/OpenTelemetry.Exporter.Zipkin/OpenTelemetry.Exporter.Zipkin.csproj
index 22b6537a7dd..3e269d83c26 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/OpenTelemetry.Exporter.Zipkin.csproj
+++ b/src/OpenTelemetry.Exporter.Zipkin/OpenTelemetry.Exporter.Zipkin.csproj
@@ -4,9 +4,6 @@
     <Description>Zipkin exporter for OpenTelemetry .NET</Description>
     <PackageTags>$(PackageTags);Zipkin;distributed-tracing</PackageTags>
     <MinVerTagPrefix>core-</MinVerTagPrefix>
-
-    <!-- this is temporary. will remove in future PR. -->
-    <Nullable>disable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporter.cs b/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporter.cs
index 69483d84a13..9ccfdc69041 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporter.cs
+++ b/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporter.cs
@@ -30,7 +30,7 @@ public class ZipkinExporter : BaseExporter<Activity>
     /// </summary>
     /// <param name="options">Configuration options.</param>
     /// <param name="client">Http client to use to upload telemetry.</param>
-    public ZipkinExporter(ZipkinExporterOptions options, HttpClient client = null)
+    public ZipkinExporter(ZipkinExporterOptions options, HttpClient? client = null)
     {
         Guard.ThrowIfNull(options);
 
@@ -39,7 +39,7 @@ public ZipkinExporter(ZipkinExporterOptions options, HttpClient client = null)
         this.httpClient = client ?? options.HttpClientFactory?.Invoke() ?? throw new InvalidOperationException("ZipkinExporter was missing HttpClientFactory or it returned null.");
     }
 
-    internal ZipkinEndpoint LocalEndpoint { get; private set; }
+    internal ZipkinEndpoint? LocalEndpoint { get; private set; }
 
     /// <inheritdoc/>
     public override ExportResult Export(in Batch<Activity> batch)
@@ -83,15 +83,15 @@ internal void SetLocalEndpointFromResource(Resource resource)
     {
         var hostName = ResolveHostName();
 
-        string ipv4 = null;
-        string ipv6 = null;
+        string? ipv4 = null;
+        string? ipv6 = null;
         if (!string.IsNullOrEmpty(hostName))
         {
-            ipv4 = ResolveHostAddress(hostName, AddressFamily.InterNetwork);
-            ipv6 = ResolveHostAddress(hostName, AddressFamily.InterNetworkV6);
+            ipv4 = ResolveHostAddress(hostName!, AddressFamily.InterNetwork);
+            ipv6 = ResolveHostAddress(hostName!, AddressFamily.InterNetworkV6);
         }
 
-        string serviceName = null;
+        string? serviceName = null;
         foreach (var label in resource.Attributes)
         {
             if (label.Key == ResourceSemanticConventions.AttributeServiceName)
@@ -115,9 +115,9 @@ internal void SetLocalEndpointFromResource(Resource resource)
             tags: null);
     }
 
-    private static string ResolveHostAddress(string hostName, AddressFamily family)
+    private static string? ResolveHostAddress(string hostName, AddressFamily family)
     {
-        string result = null;
+        string? result = null;
 
         try
         {
@@ -145,9 +145,9 @@ private static string ResolveHostAddress(string hostName, AddressFamily family)
         return result;
     }
 
-    private static string ResolveHostName()
+    private static string? ResolveHostName()
     {
-        string result = null;
+        string? result = null;
 
         try
         {
@@ -180,7 +180,7 @@ private sealed class JsonContent : HttpContent
 
         private readonly ZipkinExporter exporter;
         private readonly Batch<Activity> batch;
-        private Utf8JsonWriter writer;
+        private Utf8JsonWriter? writer;
 
         public JsonContent(ZipkinExporter exporter, in Batch<Activity> batch)
         {
@@ -191,13 +191,13 @@ public JsonContent(ZipkinExporter exporter, in Batch<Activity> batch)
         }
 
 #if NET
-        protected override void SerializeToStream(Stream stream, TransportContext context, CancellationToken cancellationToken)
+        protected override void SerializeToStream(Stream stream, TransportContext? context, CancellationToken cancellationToken)
         {
             this.SerializeToStreamInternal(stream);
         }
 #endif
 
-        protected override Task SerializeToStreamAsync(Stream stream, TransportContext context)
+        protected override Task SerializeToStreamAsync(Stream stream, TransportContext? context)
         {
             this.SerializeToStreamInternal(stream);
             return Task.CompletedTask;
@@ -226,7 +226,7 @@ private void SerializeToStreamInternal(Stream stream)
 
             foreach (var activity in this.batch)
             {
-                var zipkinSpan = activity.ToZipkinSpan(this.exporter.LocalEndpoint, this.exporter.options.UseShortTraceIds);
+                var zipkinSpan = activity.ToZipkinSpan(this.exporter.LocalEndpoint!, this.exporter.options.UseShortTraceIds);
 
                 zipkinSpan.Write(this.writer);
 
diff --git a/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterHelperExtensions.cs b/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterHelperExtensions.cs
index ca858c649ab..b7142b985a5 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterHelperExtensions.cs
+++ b/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterHelperExtensions.cs
@@ -39,13 +39,13 @@ public static TracerProviderBuilder AddZipkinExporter(this TracerProviderBuilder
     /// Adds Zipkin exporter to the TracerProvider.
     /// </summary>
     /// <param name="builder"><see cref="TracerProviderBuilder"/> builder to use.</param>
-    /// <param name="name">Name which is used when retrieving options.</param>
-    /// <param name="configure">Callback action for configuring <see cref="ZipkinExporterOptions"/>.</param>
+    /// <param name="name">Optional name which is used when retrieving options.</param>
+    /// <param name="configure">Optional callback action for configuring <see cref="ZipkinExporterOptions"/>.</param>
     /// <returns>The instance of <see cref="TracerProviderBuilder"/> to chain the calls.</returns>
     public static TracerProviderBuilder AddZipkinExporter(
         this TracerProviderBuilder builder,
-        string name,
-        Action<ZipkinExporterOptions> configure)
+        string? name,
+        Action<ZipkinExporterOptions>? configure)
     {
         Guard.ThrowIfNull(builder);
 
@@ -81,13 +81,13 @@ private static BaseProcessor<Activity> BuildZipkinExporterProcessor(
         {
             options.HttpClientFactory = () =>
             {
-                Type httpClientFactoryType = Type.GetType("System.Net.Http.IHttpClientFactory, Microsoft.Extensions.Http", throwOnError: false);
+                Type? httpClientFactoryType = Type.GetType("System.Net.Http.IHttpClientFactory, Microsoft.Extensions.Http", throwOnError: false);
                 if (httpClientFactoryType != null)
                 {
-                    object httpClientFactory = serviceProvider.GetService(httpClientFactoryType);
+                    object? httpClientFactory = serviceProvider.GetService(httpClientFactoryType);
                     if (httpClientFactory != null)
                     {
-                        MethodInfo createClientMethod = httpClientFactoryType.GetMethod(
+                        MethodInfo? createClientMethod = httpClientFactoryType.GetMethod(
                             "CreateClient",
                             BindingFlags.Public | BindingFlags.Instance,
                             binder: null,
@@ -95,7 +95,9 @@ private static BaseProcessor<Activity> BuildZipkinExporterProcessor(
                             modifiers: null);
                         if (createClientMethod != null)
                         {
-                            return (HttpClient)createClientMethod.Invoke(httpClientFactory, new object[] { "ZipkinExporter" });
+                            var parameters = new object[] { "ZipkinExporter" };
+                            var client = (HttpClient?)createClientMethod.Invoke(httpClientFactory, parameters);
+                            return client ?? new HttpClient();
                         }
                     }
                 }
diff --git a/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterOptions.cs b/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterOptions.cs
index bc94307351d..1f4bcd14684 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterOptions.cs
+++ b/src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterOptions.cs
@@ -40,12 +40,12 @@ internal ZipkinExporterOptions(
         Debug.Assert(configuration != null, "configuration was null");
         Debug.Assert(defaultBatchOptions != null, "defaultBatchOptions was null");
 
-        if (configuration.TryGetUriValue(ZipkinExporterEventSource.Log, ZipkinEndpointEnvVar, out var endpoint))
+        if (configuration!.TryGetUriValue(ZipkinExporterEventSource.Log, ZipkinEndpointEnvVar, out var endpoint))
         {
-            this.Endpoint = endpoint;
+            this.Endpoint = endpoint!;
         }
 
-        this.BatchExportProcessorOptions = defaultBatchOptions;
+        this.BatchExportProcessorOptions = defaultBatchOptions!;
     }
 
     /// <summary>
diff --git a/src/Shared/PooledList.cs b/src/Shared/PooledList.cs
index 043cd0a4525..77a353359a7 100644
--- a/src/Shared/PooledList.cs
+++ b/src/Shared/PooledList.cs
@@ -1,8 +1,11 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+#nullable enable
+
 using System.Buffers;
 using System.Collections;
+using System.Diagnostics.CodeAnalysis;
 
 namespace OpenTelemetry.Internal;
 
@@ -97,6 +100,7 @@ public struct Enumerator : IEnumerator<T>, IEnumerator
         private readonly T[] buffer;
         private readonly int count;
         private int index;
+        [AllowNull]
         private T current;
 
         public Enumerator(in PooledList<T> list)
@@ -107,9 +111,9 @@ public Enumerator(in PooledList<T> list)
             this.current = default;
         }
 
-        public T Current { get => this.current; }
+        public T Current => this.current;
 
-        object IEnumerator.Current { get => this.Current; }
+        object? IEnumerator.Current => this.Current;
 
         public void Dispose()
         {
diff --git a/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionExtensionsTest.cs b/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionExtensionsTest.cs
index 6e28b18d88c..14f28474176 100644
--- a/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionExtensionsTest.cs
+++ b/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionExtensionsTest.cs
@@ -19,7 +19,7 @@ public void CheckProcessTag(string key, object value)
     {
         var attributeEnumerationState = new TagEnumerationState
         {
-            Tags = PooledList<KeyValuePair<string, object>>.Create(),
+            Tags = PooledList<KeyValuePair<string, object?>>.Create(),
         };
 
         using var activity = new Activity("TestActivity");
@@ -36,11 +36,11 @@ public void CheckProcessTag(string key, object value)
     [InlineData("string", null)]
     [InlineData("bool", null)]
     [InlineData("double", null)]
-    public void CheckNullValueProcessTag(string key, object value)
+    public void CheckNullValueProcessTag(string key, object? value)
     {
         var attributeEnumerationState = new TagEnumerationState
         {
-            Tags = PooledList<KeyValuePair<string, object>>.Create(),
+            Tags = PooledList<KeyValuePair<string, object?>>.Create(),
         };
 
         using var activity = new Activity("TestActivity");
diff --git a/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionTest.cs b/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionTest.cs
index bfe69520fea..9a23ba329d4 100644
--- a/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionTest.cs
+++ b/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityConversionTest.cs
@@ -106,7 +106,7 @@ public void ToZipkinSpan_Status_ErrorFlagTest(StatusCode expectedStatusCode, str
 
         if (expectedStatusCode == StatusCode.Error)
         {
-            Assert.Contains(zipkinSpan.Tags, t => t.Key == "error" && (string)t.Value == string.Empty);
+            Assert.Contains(zipkinSpan.Tags, t => t.Key == "error" && (string?)t.Value == string.Empty);
         }
         else
         {
@@ -149,7 +149,7 @@ public void ToZipkinSpan_Activity_Status_And_StatusDescription_is_Set(ActivitySt
             Assert.Contains(
                 zipkinSpan.Tags, t =>
                 t.Key == ZipkinActivityConversionExtensions.ZipkinErrorFlagTagName &&
-                (string)t.Value == description);
+                (string?)t.Value == description);
         }
         else
         {
@@ -177,11 +177,11 @@ public void ActivityStatus_Takes_precedence_Over_Status_Tags_ActivityStatusCodeI
         // Assert.
         Assert.Equal("OK", zipkinSpan.Tags.FirstOrDefault(t => t.Key == SpanAttributeConstants.StatusCodeKey).Value);
 
-        Assert.Contains(zipkinSpan.Tags, t => t.Key == "otel.status_code" && (string)t.Value == "OK");
-        Assert.DoesNotContain(zipkinSpan.Tags, t => t.Key == "otel.status_code" && (string)t.Value == "ERROR");
+        Assert.Contains(zipkinSpan.Tags, t => t.Key == "otel.status_code" && (string?)t.Value == "OK");
+        Assert.DoesNotContain(zipkinSpan.Tags, t => t.Key == "otel.status_code" && (string?)t.Value == "ERROR");
 
         // Ensure additional Activity tags were being converted.
-        Assert.Contains(zipkinSpan.Tags, t => t.Key == "myCustomTag" && (string)t.Value == "myCustomTagValue");
+        Assert.Contains(zipkinSpan.Tags, t => t.Key == "myCustomTag" && (string?)t.Value == "myCustomTagValue");
         Assert.DoesNotContain(zipkinSpan.Tags, t => t.Key == ZipkinActivityConversionExtensions.ZipkinErrorFlagTagName);
     }
 
@@ -211,14 +211,14 @@ public void ActivityStatus_Takes_precedence_Over_Status_Tags_ActivityStatusCodeI
         Assert.Contains(
             zipkinSpan.Tags, t =>
             t.Key == ZipkinActivityConversionExtensions.ZipkinErrorFlagTagName &&
-            (string)t.Value == StatusDescriptionOnError);
+            (string?)t.Value == StatusDescriptionOnError);
         Assert.DoesNotContain(
             zipkinSpan.Tags, t =>
             t.Key == ZipkinActivityConversionExtensions.ZipkinErrorFlagTagName &&
-            (string)t.Value == TagDescriptionOnError);
+            (string?)t.Value == TagDescriptionOnError);
 
         // Ensure additional Activity tags were being converted.
-        Assert.Contains(zipkinSpan.Tags, t => t.Key == "myCustomTag" && (string)t.Value == "myCustomTagValue");
+        Assert.Contains(zipkinSpan.Tags, t => t.Key == "myCustomTag" && (string?)t.Value == "myCustomTagValue");
     }
 
     [Fact]
@@ -247,13 +247,13 @@ public void ActivityStatus_Takes_precedence_Over_Status_Tags_ActivityStatusCodeI
         Assert.Contains(
             zipkinSpan.Tags, t =>
             t.Key == ZipkinActivityConversionExtensions.ZipkinErrorFlagTagName &&
-            (string)t.Value == StatusDescriptionOnError);
+            (string?)t.Value == StatusDescriptionOnError);
         Assert.DoesNotContain(
             zipkinSpan.Tags, t =>
             t.Key == ZipkinActivityConversionExtensions.ZipkinErrorFlagTagName &&
-            (string)t.Value == TagDescriptionOnError);
+            (string?)t.Value == TagDescriptionOnError);
 
         // Ensure additional Activity tags were being converted.
-        Assert.Contains(zipkinSpan.Tags, t => t.Key == "myCustomTag" && (string)t.Value == "myCustomTagValue");
+        Assert.Contains(zipkinSpan.Tags, t => t.Key == "myCustomTag" && (string?)t.Value == "myCustomTagValue");
     }
 }
diff --git a/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityExporterRemoteEndpointTests.cs b/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityExporterRemoteEndpointTests.cs
index ddbd059c0cf..0f7c9e1bdb2 100644
--- a/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityExporterRemoteEndpointTests.cs
+++ b/test/OpenTelemetry.Exporter.Zipkin.Tests/Implementation/ZipkinActivityExporterRemoteEndpointTests.cs
@@ -45,7 +45,7 @@ public void GenerateActivity_RemoteEndpointResolution()
     public void GenerateActivity_RemoteEndpointResolutionPriority(RemoteEndpointPriorityTestCase testCase)
     {
         // Arrange
-        using var activity = ZipkinExporterTests.CreateTestActivity(additionalAttributes: testCase.RemoteEndpointAttributes);
+        using var activity = ZipkinExporterTests.CreateTestActivity(additionalAttributes: testCase.RemoteEndpointAttributes!);
 
         // Act & Assert
         var zipkinSpan = ZipkinActivityConversionExtensions.ToZipkinSpan(activity, DefaultZipkinEndpoint);
@@ -56,11 +56,11 @@ public void GenerateActivity_RemoteEndpointResolutionPriority(RemoteEndpointPrio
 
     public class RemoteEndpointPriorityTestCase
     {
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
-        public string ExpectedResult { get; set; }
+        public string? ExpectedResult { get; set; }
 
-        public Dictionary<string, object> RemoteEndpointAttributes { get; set; }
+        public Dictionary<string, object>? RemoteEndpointAttributes { get; set; }
 
         public static IEnumerable<object[]> GetTestCases()
         {
@@ -174,7 +174,7 @@ public static IEnumerable<object[]> GetTestCases()
             };
         }
 
-        public override string ToString()
+        public override string? ToString()
         {
             return this.Name;
         }
diff --git a/test/OpenTelemetry.Exporter.Zipkin.Tests/OpenTelemetry.Exporter.Zipkin.Tests.csproj b/test/OpenTelemetry.Exporter.Zipkin.Tests/OpenTelemetry.Exporter.Zipkin.Tests.csproj
index 31636f33157..fceb493d55d 100644
--- a/test/OpenTelemetry.Exporter.Zipkin.Tests/OpenTelemetry.Exporter.Zipkin.Tests.csproj
+++ b/test/OpenTelemetry.Exporter.Zipkin.Tests/OpenTelemetry.Exporter.Zipkin.Tests.csproj
@@ -2,8 +2,6 @@
   <PropertyGroup>
     <Description>Unit test project for Zipkin Exporter for OpenTelemetry</Description>
     <TargetFrameworks>$(TargetFrameworksForTests)</TargetFrameworks>
-    <!-- this is temporary. will remove in future PR. -->
-    <Nullable>disable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/test/OpenTelemetry.Exporter.Zipkin.Tests/ZipkinExporterTests.cs b/test/OpenTelemetry.Exporter.Zipkin.Tests/ZipkinExporterTests.cs
index b1481ac0541..97b90a5ec68 100644
--- a/test/OpenTelemetry.Exporter.Zipkin.Tests/ZipkinExporterTests.cs
+++ b/test/OpenTelemetry.Exporter.Zipkin.Tests/ZipkinExporterTests.cs
@@ -58,7 +58,7 @@ static void ProcessServerRequest(HttpListenerContext context)
             string requestContent = readStream.ReadToEnd();
 
             Responses.TryAdd(
-                Guid.Parse(context.Request.QueryString["requestId"]),
+                Guid.Parse(context.Request.QueryString["requestId"]!),
                 requestContent);
 
             context.Response.OutputStream.Close();
@@ -95,8 +95,8 @@ public void AddAddZipkinExporterNamedOptionsSupported()
     [Fact]
     public void BadArgs()
     {
-        TracerProviderBuilder builder = null;
-        Assert.Throws<ArgumentNullException>(() => builder.AddZipkinExporter());
+        TracerProviderBuilder? builder = null;
+        Assert.Throws<ArgumentNullException>(() => builder!.AddZipkinExporter());
     }
 
     [Fact]
@@ -151,7 +151,7 @@ public void EndpointConfigurationUsingEnvironmentVariable()
 
             var exporterOptions = new ZipkinExporterOptions();
 
-            Assert.Equal(new Uri(Environment.GetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar)).AbsoluteUri, exporterOptions.Endpoint.AbsoluteUri);
+            Assert.Equal(new Uri(Environment.GetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar)!).AbsoluteUri, exporterOptions.Endpoint.AbsoluteUri);
         }
         finally
         {
@@ -205,7 +205,7 @@ public void EndpointConfigurationUsingIConfiguration()
         };
 
         var configuration = new ConfigurationBuilder()
-            .AddInMemoryCollection(values)
+            .AddInMemoryCollection(values!)
             .Build();
 
         var options = new ZipkinExporterOptions(configuration, new());
@@ -247,13 +247,13 @@ public void UserHttpFactoryCalled()
             Assert.Equal(2, invocations);
         }
 
-        options.HttpClientFactory = null;
+        options.HttpClientFactory = null!;
         Assert.Throws<InvalidOperationException>(() =>
         {
             using var exporter = new ZipkinExporter(options);
         });
 
-        options.HttpClientFactory = () => null;
+        options.HttpClientFactory = () => null!;
         Assert.Throws<InvalidOperationException>(() =>
         {
             using var exporter = new ZipkinExporter(options);
@@ -288,7 +288,7 @@ public void UpdatesServiceNameFromDefaultResource()
 
         zipkinExporter.SetLocalEndpointFromResource(Resource.Empty);
 
-        Assert.StartsWith("unknown_service:", zipkinExporter.LocalEndpoint.ServiceName);
+        Assert.StartsWith("unknown_service:", zipkinExporter.LocalEndpoint!.ServiceName);
     }
 
     [Fact]
@@ -303,7 +303,7 @@ public void UpdatesServiceNameFromIConfiguration()
                 };
 
                 services.AddSingleton<IConfiguration>(
-                    new ConfigurationBuilder().AddInMemoryCollection(configuration).Build());
+                    new ConfigurationBuilder().AddInMemoryCollection(configuration!).Build());
             });
 
         var zipkinExporter = new ZipkinExporter(new ZipkinExporterOptions());
@@ -314,7 +314,7 @@ public void UpdatesServiceNameFromIConfiguration()
 
         zipkinExporter.SetLocalEndpointFromResource(Resource.Empty);
 
-        Assert.Equal("myservicename", zipkinExporter.LocalEndpoint.ServiceName);
+        Assert.Equal("myservicename", zipkinExporter.LocalEndpoint!.ServiceName);
     }
 
     [Theory]
@@ -331,7 +331,7 @@ public void IntegrationTest(
         bool useTestResource,
         bool isRootSpan,
         ActivityStatusCode statusCode = ActivityStatusCode.Unset,
-        string statusDescription = null,
+        string? statusDescription = null,
         bool addErrorTag = false)
     {
         Guid requestId = Guid.NewGuid();
@@ -378,7 +378,7 @@ public void IntegrationTest(
         var eventTimestamp = activity.Events.First().Timestamp.ToEpochMicroseconds();
 
         StringBuilder ipInformation = new StringBuilder();
-        if (!string.IsNullOrEmpty(exporter.LocalEndpoint.Ipv4))
+        if (!string.IsNullOrEmpty(exporter.LocalEndpoint!.Ipv4))
         {
             ipInformation.Append($@",""ipv4"":""{exporter.LocalEndpoint.Ipv4}""");
         }
@@ -446,13 +446,13 @@ public void IntegrationTest(
     internal static Activity CreateTestActivity(
        bool isRootSpan = false,
        bool setAttributes = true,
-       Dictionary<string, object> additionalAttributes = null,
+       Dictionary<string, object>? additionalAttributes = null,
        bool addEvents = true,
        bool addLinks = true,
-       Resource resource = null,
+       Resource? resource = null,
        ActivityKind kind = ActivityKind.Client,
        ActivityStatusCode statusCode = ActivityStatusCode.Unset,
-       string statusDescription = null,
+       string? statusDescription = null,
        DateTime? dateTime = null)
     {
         var startTimestamp = DateTime.UtcNow;
@@ -494,14 +494,14 @@ internal static Activity CreateTestActivity(
             new ActivityEvent(
                 "Event1",
                 eventTimestamp,
-                new ActivityTagsCollection(new Dictionary<string, object>
+                new ActivityTagsCollection(new Dictionary<string, object?>
                 {
                     { "key", "value" },
                 })),
             new ActivityEvent(
                 "Event2",
                 eventTimestamp,
-                new ActivityTagsCollection(new Dictionary<string, object>
+                new ActivityTagsCollection(new Dictionary<string, object?>
                 {
                     { "key", "value" },
                 })),
@@ -512,7 +512,7 @@ internal static Activity CreateTestActivity(
         var activitySource = new ActivitySource(nameof(CreateTestActivity));
 
         var tags = setAttributes ?
-                attributes.Select(kvp => new KeyValuePair<string, object>(kvp.Key, kvp.Value))
+                attributes.Select(kvp => new KeyValuePair<string, object?>(kvp.Key, kvp.Value))
                 : null;
         var links = addLinks ?
                 new[]
@@ -530,7 +530,7 @@ internal static Activity CreateTestActivity(
             parentContext: new ActivityContext(traceId, parentSpanId, ActivityTraceFlags.Recorded),
             tags,
             links,
-            startTime: startTimestamp);
+            startTime: startTimestamp)!;
 
         if (addEvents)
         {
diff --git a/test/OpenTelemetry.Tests/Shared/TestHttpServer.cs b/test/OpenTelemetry.Tests/Shared/TestHttpServer.cs
index 5965e5fecf4..9d86ae2a2aa 100644
--- a/test/OpenTelemetry.Tests/Shared/TestHttpServer.cs
+++ b/test/OpenTelemetry.Tests/Shared/TestHttpServer.cs
@@ -1,6 +1,8 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+#nullable enable
+
 using System.Net;
 
 namespace OpenTelemetry.Tests;
@@ -13,7 +15,7 @@ public static IDisposable RunServer(Action<HttpListenerContext> action, out stri
     {
         host = "localhost";
         port = 0;
-        RunningServer server = null;
+        RunningServer? server = null;
 
         var retryCount = 5;
         while (retryCount > 0)