I used a DB source to feed a ContextUpload in my flow.
This is the repository that shows what was coming in from the DB source
This is an the portion of the context info that shows what the variable was set to. Notice the extra set of braces  around the variable.
This is the Context Upload code
Where did the extra set of braces [ ] come from and how do I get rid of them?
Change the "dataType" property in the ContextUpload activity to String instead of the default List.