fix: Allow empty icon (None) in icon tags

[fsbraun]

No description provided.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6794a6e) 86.88% compared to head (5a69dd9) 86.88%.
Report is 1 commits behind head on master.

❗ Current head 5a69dd9 differs from pull request most recent head 06c4a59. Consider uploading reports for the commit 06c4a59 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #159   +/-   ##
=======================================
  Coverage   86.88%   86.88%           
=======================================
  Files         119      119           
  Lines        3089     3089           
  Branches      329      329           
=======================================
  Hits         2684     2684           
  Misses        299      299           
  Partials      106      106           

Files	Coverage Δ
...ms_frontend/contrib/icon/templatetags/icon_tags.py	76.92% <0.00%> (ø)

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