[TINKERPOP-2971] having order() before fold() omits an empty list in GroupStep's value traversal

• Type: Bug
• Status: Open
• Priority: Critical
• Resolution: Unresolved
• Affects Version/s: 3.6.4
• Component/s: tinkergraph
• Assignee: Unassigned
• Reporter: Norio Akagi
• Created: 19/Jul/23 19:09
• Updated: 09/Nov/23 20:01

Description

Using the modern graph,

gremlin> g.V().group().by().by(out().fold())
==>[v[1]:[v[3],v[2],v[4]],v[2]:[],v[3]:[],v[4]:[v[5],v[3]],v[5]:[],v[6]:[v[3]]]

out().fold() produces an empty list when there is no solution for out() in a value traversal of GroupStep. However if I put order() those empty lists are gone.

gremlin> g.V().group().by().by(out().order().fold())
==>[v[1]:[v[2],v[3],v[4]],v[4]:[v[3],v[5]],v[6]:[v[3]]]

I think this is not an expected behavior. 

I don't see the similar effect in by() itself

gremlin> g.V().as("a").select("a").by(out().fold())
==>[v[3],v[2],v[4]]
==>[]
==>[]
==>[v[5],v[3]]
==>[]
==>[v[3]]

gremlin> g.V().as("a").select("a").by(out().order().fold())
==>[v[2],v[3],v[4]]
==>[]
==>[]
==>[v[3],v[5]]
==>[]
==>[v[3]]

So likely this is GroupStep specific issue. We need to investigate how this occurs and fix if needed.