public void releaseParentKey(AssetKey parentKey) {
        if (parentAssetKey.get() == parentKey) {
            parentAssetKey.set(null);
        }
    }
Establishes the asset key that is used for tracking dependent assets
that have failed to load. When set, the {@link DesktopAssetManager}
gets a hint that it should suppress {@link AssetNotFoundException}s
and instead call the listener callback (if set).

@param parentKey The parent key
jme3-core/src/main/java/com/jme3/asset/ImplHandler.java