Checks for variables with None value in NLP

[dallan-keylogic]

Fixes

• Adds checks to diagnostic methods to catch uninitialized variables before running numerical diagnostics

Summary/Motivation:

This PR addresses #1522 by adding checks for uninitialized variables in the nlp object, as well as new functions in model_statistics and a new method for the DiagnosticsToolbox, display_variables_with_none_value_in_activated_constraints, to create a list of offending variables for your model.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.06%. Comparing base (d43c5dd) to head (2cd1949).

Files with missing lines	Patch %	Lines
idaes/core/util/model_diagnostics.py	88.88%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1564   +/-   ##
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  Coverage   77.06%   77.06%           
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  Files         389      389           
  Lines       62680    62706   +26     
  Branches    10276    10280    +4     
=======================================
+ Hits        48303    48324   +21     
- Misses      11939    11944    +5     
  Partials     2438     2438           

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[agarciadiego]

A typo and a change in text otherwise this looks good to me

[adam-a-a]

@dallan-keylogic Just curious--and we could easily loop through constraints ourselves--but is there another method that display problematic constraint terms for all active constraints? Unrelated to this PR, but figured I'd ask before checking.

[adam-a-a]

Or alternatively, do we have a method that simply displays a list of constraints that have been identified as having problematic terms?

[andrewlee94]

@adam-a-a There are separate methods for finding all constraints with either mismatched terms or potential cancellations. This method is here to provide more detail on one specific constraint, as displaying all information for all constraints upfront would be overwhelming.

[adam-a-a]

LGTM! The only thing that seems to be missing is adding to documentation on the new DiagnosticToolbox / model_diagnostics methods/functions. Is this already being handled by automated documentation via doc strings? If that is all we think we need, that's fine, but if there is anything additional that we think should be more explicitly described in documentation, we can make an issue to remind us of that.

[adam-a-a]

Just double-checked readthedocs and see that the automated documentation is sufficient!