Allow None as parameter value in morphpy

[Sparks29032]

When None is set for stretch,scale,smear, it will ignore these parameters. However, setting None for any other parameter would give an error. We now handle letting any parameter being None and ignore it properly in morphpy.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.93%. Comparing base (fc45fa1) to head (0bcda10).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #297   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          24       24           
  Lines        1480     1487    +7     
=======================================
+ Hits         1479     1486    +7     
  Misses          1        1           

Files with missing lines	Coverage Δ
tests/test_morphpy.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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