fix raise from None

[willmcgugan]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

Fixes #468

[codecov]

Codecov Report

Merging #480 (6ee976e) into master (d180781) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #480   +/-   ##
=======================================
  Coverage   99.50%   99.51%           
=======================================
  Files          58       58           
  Lines        4888     4901   +13     
=======================================
+ Hits         4864     4877   +13     
  Misses         24       24           

Flag	Coverage Δ
unittests	99.51% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
rich/traceback.py	99.42% <100.00%> (+0.04%)	⬆️

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