order by null is not escaped

[zxr615]

issue: #1498

[codecov-commenter]

Codecov Report

Merging #1499 (656fb99) into master (9105590) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1499   +/-   ##
=======================================
  Coverage   71.02%   71.02%           
=======================================
  Files         414      414           
  Lines       40022    40026    +4     
=======================================
+ Hits        28425    28429    +4     
  Misses       9805     9805           
  Partials     1792     1792           

Flag	Coverage Δ
go-1.14	70.95% <100.00%> (+<0.01%)	⬆️
go-1.15	70.98% <100.00%> (+0.01%)	⬆️
go-1.16	70.96% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
database/gdb/gdb_func.go	87.38% <100.00%> (+0.09%)	⬆️
os/glog/glog_logger_rotate.go	68.78% <0.00%> (-1.47%)	⬇️
os/gmutex/gmutex.go	97.36% <0.00%> (+2.63%)	⬆️

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