Add support for empty descriptions

[vhenzl]

See graphql/graphql-js#2177

Depends on #938.

[codecov]

Codecov Report

Merging #939 (4f4a635) into master (4ff4d52) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 4f4a635 differs from pull request most recent head 840a9e6. Consider uploading reports for the commit 840a9e6 to get more accurate results

@@             Coverage Diff              @@
##             master     #939      +/-   ##
============================================
- Coverage     94.23%   94.22%   -0.01%     
  Complexity       50       50              
============================================
  Files           117      117              
  Lines          9679     9670       -9     
============================================
- Hits           9121     9112       -9     
  Misses          558      558              

Impacted Files	Coverage Δ
src/Language/BlockString.php	100.00% <100.00%> (ø)
src/Language/Printer.php	99.25% <100.00%> (ø)
src/Utils/ASTDefinitionBuilder.php	90.00% <100.00%> (ø)
src/Utils/SchemaPrinter.php	98.94% <100.00%> (-0.03%)	⬇️
src/Error/Error.php	94.84% <0.00%> (-0.06%)	⬇️

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[spawnia]

Ready to go, since #938 is merged?

[vhenzl]

Ready to go.

[vhenzl]

@spawnia Could these rules like "multiline ternary" be enforced by the linter?

[simPod]

I'll set it up.