In my experience, that command is available when you have an open document. According to the screenshot you don't. Even when you have a file open it applies to the selected files in the project drawer.
Right. Also, none of the commands in the menu do anything if you don't have a file open, AFAIK.
So, if you edit the command and change the "Save:" option to 'Nothing', the Update item appears in the menu when there's no open file, but you still can't do anything with it.
Chris