GraphQL\Utils::undefined PHP Метод

    public static function undefined()
    {
        static $undefined;
        return $undefined ?: ($undefined = new \stdClass());
    }

 /**
  * Given a type and any value, return a runtime value coerced to match the type.
  */
 private static function coerceValue(Type $type, $value)
 {
     $undefined = Utils::undefined();
     if ($value === $undefined) {
         return $undefined;
     }
     if ($type instanceof NonNull) {
         if ($value === null) {
             // Intentionally return no value.
             return $undefined;
         }
         return self::coerceValue($type->getWrappedType(), $value);
     }
     if (null === $value) {
         return null;
     }
     if ($type instanceof ListOfType) {
         $itemType = $type->getWrappedType();
         if (is_array($value) || $value instanceof \Traversable) {
             $coercedValues = [];
             foreach ($value as $item) {
                 $itemValue = self::coerceValue($itemType, $item);
                 if ($undefined === $itemValue) {
                     // Intentionally return no value.
                     return $undefined;
                 }
                 $coercedValues[] = $itemValue;
             }
             return $coercedValues;
         } else {
             $coercedValue = self::coerceValue($itemType, $value);
             if ($coercedValue === $undefined) {
                 // Intentionally return no value.
                 return $undefined;
             }
             return [$coercedValue];
         }
     }
     if ($type instanceof InputObjectType) {
         $coercedObj = [];
         $fields = $type->getFields();
         foreach ($fields as $fieldName => $field) {
             if (!array_key_exists($fieldName, $value)) {
                 if ($field->defaultValueExists()) {
                     $coercedObj[$fieldName] = $field->defaultValue;
                 } else {
                     if ($field->getType() instanceof NonNull) {
                         // Intentionally return no value.
                         return $undefined;
                     }
                 }
                 continue;
             }
             $fieldValue = self::coerceValue($field->getType(), $value[$fieldName]);
             if ($fieldValue === $undefined) {
                 // Intentionally return no value.
                 return $undefined;
             }
             $coercedObj[$fieldName] = $fieldValue;
         }
         return $coercedObj;
     }
     if ($type instanceof LeafType) {
         $parsed = $type->parseValue($value);
         if (null === $parsed) {
             // null or invalid values represent a failure to parse correctly,
             // in which case no value is returned.
             return $undefined;
         }
         return $parsed;
     }
     throw new InvariantViolation('Must be input type');
 }