Fix for invalid parameter names.

[mitchdenny]

Fixes #2783

Microsoft Reviewers: Open in CodeFlow

[davidfowl]

This doesn't cover setting the values directly into the dictionary.

[mitchdenny]

No, it doesn't. We would need to either sub-class Dictionary<K, T> for that or perhaps add the following methods to the class and not expose the underlying dictionary. We'd need SetParameter(...), GetParameter(key) and GetParameters().