bug: docstring print statement bug

[cadenmyers13]

this was printing a bad docstring because we didnt handle the None case. it printed like this,

This function has been deprecated and will be removed in version 4.0.0.
Please use None.new_func instead.

Now, if new_base=None, the print statement will look like

This function has been deprecated and will be removed in version 4.0.0.
Please use new_func instead.

optionally, we can make the user always specify a base.

[cadenmyers13]

@sbillinge ready for review. The docstring print function didnt handle the None case nicely. Let me know what you think here

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (6ab0068) to head (fdca183).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #380   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           10        10           
  Lines          567       567           
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  Hits           567       567           

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