Set values containing `''` are not displayed correctly

[fulghum]

MySQL allows all set types to set their value to ''. Additionally, set types may declare that '' is a valid set value and it is then allowed to be combined with any other set values. To match MySQL's output, the explicitly included '' value should not be included in the string representation of the value, but Dolt/GMS is currently displaying it.

Repro:

create table z (pk int primary key, s1 set('','a','b','c'));
insert into z values (1, ",a,b,c"), (2, "a,b,c");
select pk, s1, cast(s1 as unsigned) from z;

With MySQL, this produces:

mysql> select pk, s1, cast(s1 as unsigned) from z;
+----+-------+----------------------+
| pk | s1    | cast(s1 as unsigned) |
+----+-------+----------------------+
|  1 | a,b,c |                   15 |
|  2 | a,b,c |                   14 |
+----+-------+----------------------+

With Dolt, it produces:

fri> select pk, s1, cast(s1 as unsigned) from z;
+----+--------+----------------------+
| pk | s1     | cast(s1 as unsigned) |
+----+--------+----------------------+
| 1  | ,a,b,c | 15                   |
| 2  | a,b,c  | 14                   |
+----+--------+----------------------+