public function getAssetType(string $assetType) : AssetTypeInterface
    {
        if (!isset($this->assetTypes[$assetType])) {
            if (isset($this->assetTypesArray[$assetType])) {
                $this->assetTypes[$assetType] = ImmutableAssetType::fromArray($assetType, $this->assetTypesArray[$assetType]);
            } else {
                $this->assetTypes[$assetType] = ImmutableAssetType::fromArray($assetType, []);
            }
        }
        return $this->assetTypes[$assetType];
    }