Allow override of constructor args and object attrs to return None

[rly]

Motivation

Fix #178

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.90%. Comparing base (316ec4b) to head (56e13b8).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1167      +/-   ##
==========================================
+ Coverage   88.88%   88.90%   +0.02%     
==========================================
  Files          45       45              
  Lines        9835     9835              
  Branches     2795     2795              
==========================================
+ Hits         8742     8744       +2     
+ Misses        776      775       -1     
+ Partials      317      316       -1     

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[rly]

This causes a few errors in PyNWB that I will investigate.

[mavaylon1]

This causes a few errors in PyNWB that I will investigate.

Is this PR okay to review or should I wait for the PyNWB errors.

[rly]

This causes a few errors in PyNWB that I will investigate.

Is this PR okay to review or should I wait for the PyNWB errors.

Please wait to merge. I haven't had time to look through these yet. If it does not make it in this upcoming release, that is OK.