[backport] fix #11440, add docs to isNil for seq types needing nilseq (#13234) [ci skip]
[backport] fix #11440, add docs to isNil for seq types needing nilseq (#13234) [ci skip]


dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim