code: @SuppressWarnings("unchecked")
      public <RT> Q union(Path<?> alias, SubQueryExpression<RT>... sq) {
          return from(UnionUtils.union(ImmutableList.copyOf(sq), (Path) alias, false));
      }
docs: Creates an union expression for the given subqueries
  
  @param <RT>
  @param alias alias for union
  @param sq subqueries
  @return the current object