There is a blank icon on my dock. Just underneath the icon is a small white triangle. I don't know how this blank icon got onto my dock, but I can't get rid of it.
When I right-click on the blank icon, there is no context menu entry to remove it, and if I drag it off the dock it just comes right back.
I don't even know what the icon represents. It has no name, and if I right-click on the icon one of the context menu entries says: Run ''
How can I get rid of this thing?
The white triangle sounds like a running indicator. If the icon is for a running app, it can't be removed from the dock while running. Try right clicking on the dock, select View and then Show Names. Does it show the name for the blank Icon under it? If so, shut down whatever it represents in Taskmanager, then remove it.
You may also be able to start up in Safe Mode and remove the icon, but if it's malware, it will be back. if so, you might want to run Rkill to kill the process, and then Malwarebytes to clean it out.