Fix Internal server error related to null values

[ckoppenhaver]

No description provided.

[codecov]

Codecov Report

Merging #627 into 8.x-3.x will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           8.x-3.x     #627   +/-   ##
========================================
  Coverage    79.11%   79.11%           
========================================
  Files          187      187           
  Lines         2949     2949           
========================================
  Hits          2333     2333           
  Misses         616      616

Impacted Files	Coverage Δ
...core/src/Plugin/GraphQL/Fields/EntityFieldBase.php	92.3% <100%> (ø)	⬆️

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[fubhy]

Thanks!