It's not clear to me what we can or should do here. This is easily reproducible by starting update-manager in an environment without a $DISPLAY, e.g. from an ssh session where the display is not forwarded.
The error message is perhaps too cryptic to be useful, so one fix might be to catch the exception and print a more helpful error message. If that fairly easy fix is enough, let me know and I'll work on that.
It's not clear to me what we can or should do here. This is easily reproducible by starting update-manager in an environment without a $DISPLAY, e.g. from an ssh session where the display is not forwarded.
The error message is perhaps too cryptic to be useful, so one fix might be to catch the exception and print a more helpful error message. If that fairly easy fix is enough, let me know and I'll work on that.