model fitting: handle empty poly order input

[kecnry]

Description

This pull request removes the traceback caused by emptying the poly_order input in the polynomial component of the model fitting plugin.

If adopted, similar logic should be applied across all number input fields across all plugins in the future (created separate ticket).

Before:

Screen.Recording.2022-01-19.at.3.44.57.PM.mov

After:

Screen.Recording.2022-01-19.at.3.43.46.PM.mov

TODO:

• determine between Any or subclassed Int solutions. If using Int, determine where to place subclass and move it.
• coverage to ensure Int subclass doesn't break from upstream changes
• create ticket to apply similar logic across all plugins
• change log?

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set? Milestone is only currently required for PRs related to Imviz MVP.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Attention: Patch coverage is 88.46154% with 3 lines in your changes missing coverage. Please review.

Project coverage is 74.03%. Comparing base (a010a5e) to head (f82c963).
Report is 2742 commits behind head on main.

Files	Patch %	Lines
...igs/default/plugins/model_fitting/model_fitting.py	72.72%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1041      +/-   ##
==========================================
+ Coverage   73.70%   74.03%   +0.33%     
==========================================
  Files          74       75       +1     
  Lines        5620     5638      +18     
==========================================
+ Hits         4142     4174      +32     
+ Misses       1478     1464      -14     

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[pllim]

Works as advertised and the solution seems elegant. Thanks!

Though probably out of scope for the sprint but in the spirit of OSS, do you think traitlets would accept your new classes if you try to submit a PR upstream? 💭

[pllim]

Is this order done such that our validate would overwrite the validate from upstream? Just curious.

[kecnry]

yes, this uses the new validate first (which then falls back on the super validate on the upstream Int/Float traitlets if the value isn't an empty string).

[rosteen]

Looks good, I appreciate the addition of form validation guidance to the developer docs. I know I've tried to be good about using that in the past but haven't been totally consistent.