Removing extension for Name of document in SharePoint

Hi

Working on-prem, with Nintex workflow 2013.

I am trying to remove the extension of a document name

Example Test.docx or Test.pdf

What l did was use a Regular expression using the item column (Name) to extract using Pattern :

 [^/]*(?=.[^.]+($|?)) into a collection variable CollTest1

then used a numeric variable 1 (Also tried 0 same issue) to get the first collection but when l run the workflow get the following error :

Error operating on collection variable. Index property is greater than the number of items in the collection.

Thanks