I've also had this error when trying to pull the changes into a branch which is not created from the upstream branch from which I'm trying to pull.
Eg - This creates a new branch matching night-version
of upstream
git checkout upstream/night-version -b testnightversion
This creates a branch testmaster
in local which matches the master
branch of upstream.
git checkout upstream/master -b testmaster
Now if I try to pull the changes of night-version
into testmaster
branch leads to this error.
git pull upstream night-version //while I'm in `master` cloned branch
I managed to solve this by navigating to proper branch and pull the changes.
git checkout testnightversion
git pull upstream night-version // works fine.