Screen sharing only working when monitor connected

Using Ubuntu 19.04, I can only use the built-in screen sharing (vino) when a monitor is connected. I can successfully connect even without a monitor connected, but the screen isn't updated (ie I see the screen as it was the moment I disconnected the monitor.

How do I solve this?


It doesn't feel like the most elegant solution but this issue was solved for me by one of those HDMI dummy plugs which emulates a connected screen. They can be picked up for about $10.

I've found the wide range of resolutions they spoof to be handy.