✨ Improve exception message for unexpected null value - mention expected type

[andrew-demb]

In our case, we attempted to investigate the reason for the error "Unexpected null value for non nullable field" for the array output field (and all PHP types were returning an array). But the real reason was about array elements - we returned null instead of a string - aka array('foobar', null) instead of array('foobar') - because of array<string> phpdoc over the output field method.

---

Before:

In Acme\Graphql\Type\FooType::getButtons() (declaring field "buttons"): Unexpected null value for non nullable field.

After:

In Acme\Graphql\Type\FooType::getButtons() (declaring field "buttons"): Unexpected null value for non nullable field. Expected: "String!".

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.79%. Comparing base (53f9d49) to head (3becc34).
⚠️ Report is 124 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #762      +/-   ##
============================================
- Coverage     95.72%   94.79%   -0.94%     
- Complexity     1773     1846      +73     
============================================
  Files           154      175      +21     
  Lines          4586     5014     +428     
============================================
+ Hits           4390     4753     +363     
- Misses          196      261      +65     

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[andrew-demb]

CI failure is unrelated

With the provided path, there will be 282 files uploaded
Artifact name is valid!
Root directory input is valid!
Error: Failed to CreateArtifact: Received non-retryable error: Failed request: (409) Conflict: an artifact with this name already exists on the workflow run

[oojacoboo]

Thanks @andrew-demb