Shouldn't trim fields when it's under Union

String sql =
    "select \n"
    + "   gender, \n"
    + "   count(*) \n"
    + "from \n"
    + "(\n"
    + "  (select gender, empno from EMPS) \n"
    + "  union \n"
    + "  (select gender, empno from EMPS)\n"
    + ") group by gender";

EnumerableAggregate(group=[{0}], EXPR$1=[COUNT()])
  EnumerableUnion(all=[false])
    EnumerableProject(GENDER=[$3])
      EnumerableTableScan(table=[[SALES, EMPS]])
    EnumerableProject(GENDER=[$3])
      EnumerableTableScan(table=[[SALES, EMPS]])