Raise UnknownType exception with better error message.

[python-desert]

No description provided.

[codecov-io]

Codecov Report

Merging #8 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master      #8      +/-   ##
=========================================
+ Coverage   95.39%   95.5%   +0.11%     
=========================================
  Files           6       6              
  Lines         326     334       +8     
  Branches       58      60       +2     
=========================================
+ Hits          311     319       +8     
  Misses          9       9              
  Partials        6       6

Impacted Files	Coverage Δ
tests/test_make.py	97.64% <100%> (+0.07%)	⬆️
src/desert/_version.py	100% <100%> (ø)	⬆️
src/desert/_make.py	91.4% <100%> (+0.13%)	⬆️
src/desert/exceptions.py	100% <100%> (ø)	⬆️

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