Neos.Media/Classes/Domain/Model/AssetCollection.php
public function addAsset(Asset $asset): bool
    {
        if ($asset->getAssetCollections()->contains($this) === false) {
            $this->assets->add($asset);
            return true;
        }

        return false;
    }
public function addAsset(Asset $asset): bool
    {
        if ($asset->getAssetCollections()->contains($this) === false) {
            $this->assets->add($asset);
            return true;
        }

        return false;
    }
public function addAsset ( Asset $ asset ) : bool { if ( $ asset -> getAssetCollections ( ) -> contains ( $ this ) === false ) { $ this -> assets -> add ( $ asset ) ; return true ; } return false ; }
Add one asset to the asset collection

@param Asset $asset
@return bool
Add one asset to the asset collection