expression: fix unexpected panic when doing isNullRejected check (#22173)#22327

Merged

qw4990 merged 4 commits intopingcap:release-4.0from ti-srebot:release-4.0-cdcb0ffa3412

Jan 14, 2021

+33-33

Commits on Jan 11, 2021

cherry pick pingcap#22173 to release-4.0

xuyifangreeneyes
authored and
ti-srebot
committed

Commits on Jan 14, 2021