public boolean hasEmptyPath() {
		// since EMPTY_RETURN_STATE can only appear in the last position, we check last one
		return getReturnState(size() - 1) == EMPTY_RETURN_STATE;
	}
This means only the {@link EmptyPredictionContext#Instance} (wildcard? not sure) context is in set.
runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java