fix: more robust nil check for link transformer

[danielgtaylor]

This uses reflection to check for nil which is more robust and can prevent a panic/500 error from happening if the operation returns successful with a nil body.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.71%. Comparing base (babafa8) to head (7f74b7d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
+ Coverage   92.65%   92.71%   +0.05%     
==========================================
  Files          21       21              
  Lines        3539     3540       +1     
==========================================
+ Hits         3279     3282       +3     
+ Misses        221      220       -1     
+ Partials       39       38       -1     

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