How do we define empty value

[czpmango]

Describe the bug (required)
We need to define the exact semantics of empty and null to avoid inconsistent statement behavior.

Your Environments (required)
nebula all versions

How To Reproduce(required)

(root@nebula) [nba]> go from "Tim Duncan" over * yield $$.team.name
+--------------+
| $$.team.name |
+--------------+
|              |
|              |
| "Spurs"      |
|              |
|              |
|              |
|              |
+--------------+
Got 7 rows (time spent 3690/4030 us)

(root@nebula) [nba]> match (v)-[]->(n) where id(v)=="Tim Duncan" return n.team.name
+-------------+
| n.team.name |
+-------------+
| "Spurs"     |
| __NULL__    |
| __NULL__    |
| __NULL__    |
| __NULL__    |
| __NULL__    |
| __NULL__    |
+-------------+

Expected behavior
The expectation is to ensure consistent behavior of statements

Additional context
Similarly, there are other null-compatible value types to consider, such as UNKNOWN_PROP, etc.

[czpmango]

@MuYiYong cc

[czpmango]

@yixinglu cc

[xtcyclist]

This is a good issue. It has broad impacts. Need to make an conclusion on this.

[Sophie-Xie]

Discuss it offline with @MuYiYong @yixinglu @HarrisChu: Remain current behavior.

[czpmango]

Discuss it offline with @MuYiYong @yixinglu @HarrisChu: Remain current behavior.

Ok.