Pipe rank with agg func error

[BOFA1ex]

Describe the bug (required)

go from "10a2a268-618f-40aa-90df-bda58eb169b8" over * yield src(edge) as src, dst(edge) as dst, rank(edge) as rank 
| yield $-.src as src, $-.dst as dst, max($-.rank) as rank 
| fetch prop on lineage_trace_edge $-.src -> $-.dst @$-.rank yield edge as e

Actually, YIELD max($-.rank) as rank has been returned INT value yet.

Console Log

-1009:SemanticError: `$-.rank' should be type of INT, but was __EMPTY__

Your Environments (required)

• OS: Linux nebula2 3.10.0-1160.el7.x86_64 #1 SMP Mon Oct 19 16:18:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• Compiler: g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
• CPU: lscpu
• Commit id 02b2091