Fix strict PHP warnings after a fresh install.

[justin-longbottom]

After a fresh install of the module, the create server form has a few errors and warnings.

Notice: Undefined index: schema in Drupal\graphql\Form\ServerForm->form() (line 92 of modules/contrib/graphql/src/Form/ServerForm.php).
Drupal\graphql\Form\ServerForm->form(Array, Object) (Line: 117)

Notice: Only variables should be passed by reference in Drupal\graphql\Form\ServerForm->form() (line 92 of modules/contrib/graphql/src/Form/ServerForm.php).
Drupal\graphql\Form\ServerForm->form(Array, Object) (Line: 117)

Notice: Undefined index: #options in Drupal\Core\Render\Element\Checkboxes::processCheckboxes() (line 58 of core/lib/Drupal/Core/Render/Element/Checkboxes.php).

Warning: count(): Parameter must be an array or an object that implements Countable in Drupal\Core\Render\Element\Checkboxes::processCheckboxes() (line 58 of core/lib/Drupal/Core/Render/Element/Checkboxes.php).

[codecov]

Codecov Report

Merging #878 into 8.x-4.x will decrease coverage by 0.05%.
The diff coverage is 0%.

@@              Coverage Diff              @@
##             8.x-4.x     #878      +/-   ##
=============================================
- Coverage      66.43%   66.38%   -0.06%     
  Complexity       587      587              
=============================================
  Files             92       92              
  Lines           1299     1300       +1     
=============================================
  Hits             863      863              
- Misses           436      437       +1

Impacted Files	Coverage Δ	Complexity Δ
src/Plugin/GraphQL/Schema/ComposableSchema.php	0% <0%> (ø)	11 <0> (ø)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 526eeea...d754460. Read the comment docs.

[mkochendorfer]

The PR fixed the errors for me as well.

[sebas5384]

Thanks! this PR worked 👍

[fubhy]

Thanks. I adjusted the fix according to klausi's suggestion.

[vouza]

I still receive the error Notice: Undefined index: schema in Drupal\graphql\Form\ServerForm->form()
$arr = array_keys($schemas); $schema = ($inputSchema ?? $server->get('schema')) ?: reset($arr);
should fix it.