Improve error message on EmptyConstraint

[ChrisMaddock]

When EmptyConstraint is used on the incorrect type, it throws the following exception:

throw new System.ArgumentException("The actual value must be a string or a non-null IEnumerable or DirectoryInfo", nameof(actual));

When chaining constraints, I sometimes hit this error message because of problems in my chaining, where I'm actually testing against a different type to the one I think I am. It would be useful if this error message included the type of actual which caused the exception - so the user can better debug where the problem in their chaining lies.

Ideally, whoever contributes this functionality would also add a corresponding unit test! There may already be something there - I haven't checked. 🙂

[nisha-kaushik]

Hey, I want to pick this up for contribution. Can you please explain it with some example.

[ChrisMaddock]

@nisha-kaushik Great!

Take a look at this pull request below, where I made a very similar change to PropertyConstraint, to the one we want to make to EmptyConstraint. Do you want to have a go at a similar change to EmptyConstraint, and then put up a pull request, and we can work from there?

#2739

I've assigned this issue to myself to keep an eye on - let us know if you have any further questions, and we'll help where we can! 👍

[nisha-kaushik]

Thanks @ChrisMaddock I made some changes in pull request #2961.

Please Let me know in case of changes.