xfce4-terminal stops working on empty user command

How to reproduce:

In the settings for xfce4.-terminal select "User defined command insteall of shell" and leave the text field empty.

When starting the terminal, or opening a new tab, you get an error message like "could not start child process". If you click ok, you get a terminal window, but you cannot type in this window.

Impact:

Not a big problem, but I clicked on the setting by accident, and didn't even realize I had checked it. I was very suprised that suddenly I could not use my xfce4-terminal anymore, and it took me a while to find the problem. In fact I was surprised how fast I spotted the problem in the end. Probably puzzling for anyone who runs into this.

Proposal for improvement:

It would be a good idea to check for an empty string in the field - maybe even give some visual feedback that the field is empty in the settings editor. An empty command string probably is not what the user intended, so give a more informative error message like "not executing empty command". I guess the current error message does not come from xfce4-terminal, but from trying to start a process with an empty name.