Change in query "distinct" flag type from bool|null to bool

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	✔️

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.19%. Comparing base (0cf5777) to head (5256771).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #972      +/-   ##
============================================
+ Coverage     99.14%   99.19%   +0.05%     
  Complexity     1611     1611              
============================================
  Files            98       98              
  Lines          3976     3980       +4     
============================================
+ Hits           3942     3948       +6     
+ Misses           34       32       -2     

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