How to test if String Parameter is empty in a Formula?

How do I test if a String Parameter in a process has not been filled in using a Formula?  For example, the following are not working because they do not evaluate to true when the parameter is not filled in:

[#MyStringParameter#]==""
 
[#MyStringParameter#]==String.Empty

Is there a function for String length?

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I've used the following: 

string.IsNullOrEmpty([#MyStringParameter#])

However, I believe I've used what you're using as well (but might have wrapped it in parentheses)

Ryan Farley,

String.IsNullOrEmpty([#MyStringParameter#]) works.  Thanks!

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