#202 add possibility of body not required

[phantom943]

Description:

Closes #202

Checklist

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

[phantom943]

After https://github.com/caronc/apprise/pull/1163 has been merged, this is not necessary