Support an empty grouping expression

postgres=# create table gstest2 (a integer, b integer, c integer, d integer, e integer, f integer, g integer, h integer);
postgres=# insert into gstest2 values
postgres-#   (1, 1, 1, 1, 1, 1, 1, 1),
postgres-#   (1, 1, 1, 1, 1, 1, 1, 2),
postgres-#   (1, 1, 1, 1, 1, 1, 2, 2),
postgres-#   (1, 1, 1, 1, 1, 2, 2, 2),
postgres-#   (1, 1, 1, 1, 2, 2, 2, 2),
postgres-#   (1, 1, 1, 2, 2, 2, 2, 2),
postgres-#   (1, 1, 2, 2, 2, 2, 2, 2),
postgres-#   (1, 2, 2, 2, 2, 2, 2, 2),
postgres-#   (2, 2, 2, 2, 2, 2, 2, 2);
INSERT 0 9

postgres=# select v.c, (select count(*) from gstest2 group by () having v.c) from (values (false),(true)) v(c) order by v.c;
 c | count 
---+-------
 f |      
 t |    18
(2 rows)

scala> sql("""select v.c, (select count(*) from gstest2 group by () having v.c) from (values (false),(true)) v(c) order by v.c""").show
org.apache.spark.sql.catalyst.parser.ParseException:
no viable alternative at input '()'(line 1, pos 52)

== SQL ==
select v.c, (select count(*) from gstest2 group by () having v.c) from (values (false),(true)) v(c) order by v.c
----------------------------------------------------^^^

  at org.apache.spark.sql.catalyst.parser.ParseException.withCommand(ParseDriver.scala:268)
  at org.apache.spark.sql.catalyst.parser.AbstractSqlParser.parse(ParseDriver.scala:135)
  at org.apache.spark.sql.execution.SparkSqlParser.parse(SparkSqlParser.scala:48)
  at org.apache.spark.sql.catalyst.parser.AbstractSqlParser.parsePlan(ParseDriver.scala:85)
  at org.apache.spark.sql.SparkSession.$anonfun$sql$1(SparkSession.scala:605)
  at org.apache.spark.sql.catalyst.QueryPlanningTracker.measurePhase(QueryPlanningTracker.scala:111)
  at org.apache.spark.sql.SparkSession.sql(SparkSession.scala:605)
  ... 47 elided