Improve PaddingConverter CreateInstance implementation

[weltkante]

Fixes #2677

Proposed changes

• The context argument may be null for callers other than the PropertyGrid, this should not lead to an exception, in particular since GetCreateInstanceSupported returns true for a null context. Also every other implementation of CreateInstance I could find in WinForms and System.Drawing supports a null context, so PaddingConverter is an outlier.

Regression?

• No

Risk

• Callers which depend on an exception being thrown in a previously unsupported scenario will no longer see an exception

Before

• PaddingConverter.CreateInstance(null, properties) throws an exception even though PaddingConverter.GetCreateInstanceSupported(null) returns true

After

• PaddingConverter.CreateInstance(null, properties) creates an instance based on the given properties like any other TypeConverter defined in WinForms and System.Drawing

Test methodology

• Tests have not been updated yet, this is WIP for discussion

Microsoft Reviewers: Open in CodeFlow

[RussKie]

I think this is a sensible proposal.
Looks like all other converters do the right thing and use context if it's not null. None of them throw.
Though it appears we have few more possible NREs related to use of context in MdiWindowListItemConverter and LanguageCultureInfoConverter.

On a side note, a number of UITypeEditors appear to like to live dangerously and use context without checks for null.

[RussKie]

I'm curious, is this reachable at all?

            catch (NullReferenceException nullRef)
            {
                throw new ArgumentException(SR.PropertyValueInvalidEntry, nameof(propertyValues), nullRef);
            }

[weltkante]

I'm curious, is this reachable at all?

You get this instead of a typecast exception when a value is null; also values are null for missing keys when the caller uses a Hashtable to store the properties.

[weltkante]

Updated the tests. I think the existing tests (with updated expectations) already cover the modified code paths sufficiently.

[codecov]

Codecov Report

Merging #2679 into master will increase coverage by 0.563%.
The diff coverage is 100%.

@@                 Coverage Diff                 @@
##              master       #2679         +/-   ##
===================================================
+ Coverage   57.59523%   58.15824%   +0.56301%     
===================================================
  Files           1235        1240          +5     
  Lines         418368      423008       +4640     
  Branches       38816       38852         +36     
===================================================
+ Hits          240960      246014       +5054     
+ Misses        172035      171620        -415     
- Partials        5373        5374          +1

Flag	Coverage Δ
#Debug	58.15824% <100%> (+0.563%)	⬆️
#production	31.49243% <ø> (+0.17304%)	⬆️
#test	98.92984% <100%> (-0.00364%)	⬇️

[RussKie]

Thank you