Null pointer error on software update

Saw there was an update this morning, went to install it and got the following error:

Unable to update “(null)”: GDBus.Error.org.gtk.GDBus.UnmappedGError.Quark._pk_2dengine_2error_2dquark.Code1.Prepared update not found: /var/lib/PackageKit/prepared-update

Was that from the GNOME Software GUI or from the command line? My guess is GUI, in which case, I suspect you can still retrieve updates via

sudo apt update
sudo apt upgrade

at the command line.

Alternatively, I would suggest trying

sudo service packagekit restart

and trying the GUI again. I’ve had issues with the GUI messing up because of a stalled packagekit, and I see packagekit mentioned in your error.

Thanks for the suggestions. Yes, the error was from the Software GUI. I did a reboot, and that seems to have cleared the problem, but I have added the packagekit restart command to my list of handy tools.

Recently I have updated the software and encountered an error just after that. When I was going to print my canon printer offline windows 10 was popping up everytime so please help me with the proper solution.

It may be worth starting a new thread with more details of your problem. You’ve linked to a page regarding Windows 10 support, which doesn’t seem relevant to me