question: public static Collection < UUID > nodeIds ( @ Nullable Collection < ? extends ClusterNode > nodes ) { if ( nodes == null || nodes . isEmpty ( ) ) return Collections . emptyList ( ) ; return F . viewReadOnly ( nodes , node2id ( ) ) ; }
target:  Convenient utility method that returns collection of node IDs for a given collection of grid nodes. <p> Note that this method doesn't create a new collection but simply iterates over the input one.