public function getAssociationCollectionClass(string $assocName) : string
    {
        if (! isset($this->associationMappings[$assocName])) {
            throw new InvalidArgumentException("Association name expected, '" . $assocName . "' is not an association.");
        }

        if (! array_key_exists('collectionClass', $this->associationMappings[$assocName])) {
            throw new InvalidArgumentException("collectionClass can only be applied to 'embedMany' and 'referenceMany' associations.");
        }

        return $this->associationMappings[$assocName]['collectionClass'];
    }