An unexpected message box appears on adding a folder to a dataset widget

Scenario to reproduce:

1. Open Workflow Designer.
2. Put "Read Alignment" element to the scene. Select it.
3. Click "Add folder" button on the dataset widget toolbar on the Properties editor.
4. Do not select anything, choose a default folder.
   Expected state: current folder is added to the dataset.
   Current state: a message box appears:

   This file or directory does not exist: /Users/atiunov/root/untitled

   The "Select folder" dialog thinks that "untitled" folder is selected by default.