[5.x] Handle null value gracefully

[aerni]

I've encountered a scenario where $resolved is null. Resulting in Call to a member function value() on null. This can happen when $value->value() in resolveGqlValue() is null.

cms/src/GraphQL/ResolvesValues.php

Lines 12 to 16 in eaa66b5

	$value = $this->augmentedValue($field);
	if ($value instanceof Value) {
	$value = $value->value();
	}