'Boolean System.String.IsNullOrWhiteSpace(System.String)'

'Boolean System.String.IsNullOrWhiteSpace(System.String)'

Hello everyone, 

Im creating an extension, and I'm getting the following error:

Method not found: 'Boolean System.String.IsNullOrWhiteSpace(System.String)'.

anyone has an ideia for the reason of this error? 

The extension is published without any problems, and when i try to use it i always get this error.
In the extension the method presents no problem.

Can you share the complete extension or at least the code?

It could be anything afaik


I found the problem already, i forgot to post the answer and indeed the post is incomplete. The .NET extension that i was changing to use was built in 4.0, the error was generated cause the methods that i was trying to access didn't exist :)

Sorry for the trouble.