src/Type/Definition/NonNull.php
public static function assertNullableType($type)
    {
        Utils::invariant(
            Type::isType($type) && ! $type instanceof self,
            'Expected ' . Utils::printSafe($type) . ' to be a GraphQL nullable type.'
        );

        return $type;
    }
public static function assertNullableType($type)
    {
        Utils::invariant(
            Type::isType($type) && ! $type instanceof self,
            'Expected ' . Utils::printSafe($type) . ' to be a GraphQL nullable type.'
        );

        return $type;
    }
@param mixed $type

@return NullableType