- Previously `ModelBindingResult.IsModelSet` would be set to true if type conversions resulted in empty => `null` values for ValueTypes. This resulted in improper usage of `ModelBindingResult`s creating null ref exceptions in certain cases.
- Updated existing functional test to account for new behavior. Previously it was handling the null ref exception by stating that errors were simply invalid; now we can provide a more distinct error.
- Added unit test to validate `TypeConverterModelBinder` does what it's supposed to when conversions result in null values.
- Added additional integration tests for `TypeConverterModelBinder`.
#2720
