Empty tag endpoint returns an incorrect result

[czpmango]

Describe the bug (required)

Empty tag endpoint returns an incorrect result

Your Environments (required)

Version: v2.6.0

How To Reproduce(required)

Steps to reproduce the behavior:

(czp@nebula) [nba]> create tag B()
Execution succeeded (time spent 1781/2075 us)

(czp@nebula) [nba]> insert vertex B() values "1":()
Execution succeeded (time spent 3505/3783 us)

(czp@nebula) [nba]> INSERT edge like(likeness) values "Tim Duncan"->"1":(97)
Execution succeeded (time spent 3751/4058 us)

(czp@nebula) [nba]> go from "Tim Duncan" over like where like.likeness>95 yield like._dst as dst1,$$ as dst2
+------+------+
| dst1 | dst2 |
+------+------+
| "1"  |      |
+------+------+
Got 1 rows (time spent 5686/6114 us)

(czp@nebula) [nba]> create tag C(a int)
Execution succeeded (time spent 1683/1988 us)

(czp@nebula) [nba]> insert vertex C(a) values "2":(3)
Execution succeeded (time spent 3186/3509 us)

(czp@nebula) [nba]> insert edge like(likeness) values "Tim Duncan"->"2":(97)
Execution succeeded (time spent 3031/3359 us)

(czp@nebula) [nba]> go from "Tim Duncan" over like where like.likeness==97 yield like._dst as dst1,$$ as dst2
+------+----------------+
| dst1 | dst2           |
+------+----------------+
| "1"  |                |
+------+----------------+
| "2"  | ("2" :C{a: 3}) |
+------+----------------+

Expected behavior

(czp@nebula) [nba]> go from "Tim Duncan" over like where like.likeness==97 yield like._dst as dst1,$$ as dst2
+------+----------------+
| dst1 | dst2           |
+------+----------------+
| "1"  |     ("1":B{})  |
+------+----------------+
| "2"  | ("2" :C{a: 3}) |
+------+----------------+

[Shylock-Hg]

Interesting. $$ as dst2 should result an syntax error.

[nevermore3]

fix in #3335