isAssociationNullable example

if (null === $metadata = $this->getMetadata($class)) {
            return null;
        }

        if ($metadata->hasAssociation($property)) {
            $class = $metadata->getAssociationTargetClass($property);

            if ($metadata->isSingleValuedAssociation($property)) {
                if ($metadata instanceof ClassMetadataInfo) {
                    $associationMapping = $metadata->getAssociationMapping($property);

                    $nullable = $this->isAssociationNullable($associationMapping);
                } else {
                    $nullable = false;
                }

                return [new Type(Type::BUILTIN_TYPE_OBJECT, $nullable, $class)];
            }

            $collectionKeyType = Type::BUILTIN_TYPE_INT;

            if ($metadata instanceof ClassMetadataInfo) {
                $associationMapping = $metadata->getAssociationMapping($property);