Passing nullptr for ChangedVids/ChagnedElementIDs/ChangedConnectivityTids means that all vids/elements/tids need updating, respectively. Passing UUVEditorToolMeshInput::NONE_CHANGED_ARG is equivalent to passing a pointer to an empty array, and means that none changed. Otherwise only the vids/elements/tids in the pointed-to arrays are iterated over in the updated mesh. While passing these allows updates to be quicker, note that failing to include the relevant tids/vids/elements can put the input object into an invalid state or hit a check, for instance if a triangle refers to a new vid that was not added in.