Workflows: check if picklist is not null

I am trying to figure out why an integration event won't trigger. I want to have it so that if one picklist contains the desired criteria and another field is not empty, then to fire an integration. My workflow works when I enter the first criteria but when I enter the second part (check if other field is empty), it doesn't work. Here is what I have so far:

ExcludeChannel("Web Services") and ([<IndexedPick4>] <> "N" or [<IndexedPick4>] IS NULL) and ((([<Type>] = "Sales" or [<Type>] = "Conference" or [<Type>] = "Training" or [<Type>] = "Presentation") and [<Account>] IS NOT NULL))

The last part is not working for me. Can someone please advise?