fix: missing targeting key should return null

[liran2000]

Problem:
getTargetingKey of missing targeting key causing NullPointerException.
Solution:
getTargetingKey of missing targeting key returns null.

failing java-sdk-contrib CI:

Error:  dev.openfeature.contrib.providers.flagd.resolver.process.targeting.OperatorTest.timestampPresent -- Time elapsed: 0.006 s <<< ERROR!
java.lang.NullPointerException
	at dev.openfeature.sdk.ImmutableContext.getTargetingKey(ImmutableContext.java:65)
	at dev.openfeature.contrib.providers.flagd.resolver.process.targeting.Operator.apply(Operator.java:52)

When adopting #805, saw an issue when checking missing targeting key when it is required, causing the check to not work properly:

if (ctx.getTargetingKey() == null) {
    throw new TargetingKeyMissingError("targeting key is required.");
}

Related test check can be updated after this fix.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.52%. Comparing base (433f94a) to head (3c9c301).

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #849      +/-   ##
============================================
+ Coverage     95.15%   95.52%   +0.36%     
- Complexity      367      371       +4     
============================================
  Files            34       34              
  Lines           847      849       +2     
  Branches         50       52       +2     
============================================
+ Hits            806      811       +5     
+ Misses           22       20       -2     
+ Partials         19       18       -1     

Flag	Coverage Δ
unittests	95.52% <100.00%> (+0.36%)	⬆️

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[Kavindu-Dodan]

@liran2000 thanks a lot for the NPE fix :)

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud