allow empty body when attachment is provided

[gera2ld]

Description:

Related issue (if applicable): refs #

When an attachment is provided, body should be optional. At least this is how the command-line works.

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• No lint errors (use flake8)
• Tests added

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9d3f8c7) 95.23% compared to head (c6e4a57) 95.23%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #156   +/-   ##
=======================================
  Coverage   95.23%   95.23%           
=======================================
  Files           7        7           
  Lines         714      714           
=======================================
  Hits          680      680           
  Misses         34       34           

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