Open URL action is not working!

If I select something in OmniGraffle, I can NOT choose “Open a URL” for it. It will switch back to “No Action” or “Jump to…” automatically.
I noticed that the other options in “Action” are NOT selectable as well. (E.g, Open a File or Run AppleScript)
My OmniGraffle Version Number: 7.7.1 (v186.9 r304876)
Mac OS Version: 10.13.3
I believe this bug happens a lot in different user’s Mac.
Here’s a old post: Open URL action not working

Once you choose a selection, like a URL or an Apple Script, enter a URL or a script in the dialog below your selection. If you do not enter a URL or a script to run, the action is incomplete and it will not save.

For example: If you choose Open a URL, you enter below what the URL is, like and then that action will be saved. If I just pick “Run AppleScript” but do not enter any AppleScript to run below, there is no valid action, so it returns to “No Action”. That is because no script was specified to run on the selected graphic.

The area highlighted in Orange in this image is where the text should be entered: ActionEntered

If you are setting the text in the Properties Inspector below the action selection dropdown, but your completed action is not being saved, that is a problem we can’t reproduce. Please choose Contact Omni under the Help menu and we will try to isolate the issue and get this working for you.