expression: handle empty input and improve compatibility for `format` (#8797)#9235

Merged

zz-jason merged 1 commit intopingcap:release-2.1from zz-jason:cherrpick/2.1-kenan-format

Feb 1, 2019

+117-54

Commits on Jan 31, 2019

expression: handle empty input and improve compatibility for format (pingcap#8797 )

eurekaka
authored and
zz-jason
committed