Empty target in profiles.yml results in an unhelpful error message

[clrcrl]

Steps to reproduce

1. Create a profile like so (note empty learn: key)

$ cat ~/.dbt/profiles.yml
jaffle_shop:
  target: learn

  outputs:
    learn:

2. Run dbt debug --profile jaffle_shop

Expected behavior

A useful error message

Actual behavior

$ dbt debug --profile jaffle_shop
Running with dbt=0.18.0-b1
dbt version: 0.18.0-b1
python version: 3.7.5
python path: /Users/claire/.pyenv/versions/3.7.5/envs/dbt-dev-v2/bin/python
os info: Darwin-19.4.0-x86_64-i386-64bit
Using profiles.yml file at /Users/claire/.dbt/profiles.yml
Using dbt_project.yml file at /Users/claire/clrcrl/jaffle_shop/dbt_project.yml

Encountered an error:
'NoneType' object has no attribute 'pop'

The output of dbt --version:

$ dbt --version
installed version: 0.18.0-b1
   latest version: 0.17.0

Your version of dbt is ahead of the latest release!

Plugins:
  - bigquery: 0.18.0b1
  - snowflake: 0.18.0b1
  - redshift: 0.18.0b1
  - postgres: 0.18.0b1

Additional context

This came up because someone had their profile indented incorrectly:

jaffle_shop:
  target: learn

  outputs:
    learn:
    type: snowflake
    threads: 1
    account: ***
    ...

[kning]

just an fyi, im working on this now