fix: decorator job with no inner function

[yitchen-tim]

Description of changes:
Skip copying inner function source to decorator job when there is no inner function. The job interface did not handle empty input gracefully.

Testing done:
tox

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (b533b89) to head (e550590).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1061   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          135       135           
  Lines         9085      9087    +2     
  Branches      1045      1046    +1     
=========================================
+ Hits          9085      9087    +2     

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