Treat empty fullUrl as null/missing

[breedx-splk]

Minor improvement after #1723, which slightly changed how an empty configuration string would be handled.

Prior to #1723 we would check for empty before falling back. This same approach needs to also happen with the fullUrl, so that if a user configures an empty string as a fullUrl, we still just use the locally scoped url.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.61%. Comparing base (e6ec3c1) to head (5c2a63e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1749   +/-   ##
=======================================
  Coverage   61.61%   61.61%           
=======================================
  Files         158      158           
  Lines        3423     3423           
  Branches      345      345           
=======================================
  Hits         2109     2109           
  Misses       1217     1217           
  Partials       97       97           

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[fractalwrench]

LGTM