@Override
	public boolean isEmpty() {
		// since EMPTY_RETURN_STATE can only appear in the last position, we
		// don't need to verify that size==1
		return returnStates[0]==EMPTY_RETURN_STATE;
	}
Sorted for merge, no duplicates; if present,
 {@link #EMPTY_RETURN_STATE} is always last.
runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java