Add method return type to MapEverywhere

[isc-pbarton]

Suggested in #772
No changelog needed as there is no functional change.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.20%. Comparing base (7b9913d) to head (2f74974).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #773   +/-   ##
=======================================
  Coverage   41.20%   41.20%           
=======================================
  Files          24       24           
  Lines        3233     3233           
=======================================
  Hits         1332     1332           
  Misses       1901     1901           

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