fix: the logic for getting the handler

[Champgy]

First, get the handler from the specified namespace. If the handler is None, then get the handler from the namespace *.
#1315

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (fff4640) to head (569fdb4).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1316   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files           31        31           
  Lines         2449      2449           
  Branches       431       431           
=========================================
  Hits          2449      2449           

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[miguelgrinberg]

Thanks!