Migration V4 to V5 Error - Command 'git fetch upstream' returned non-zero exit status 128

erpnext@erpnext:~/frappe-bench$ bench update --upgrade
Already up-to-date.
fatal: Invalid refspec ‘+refs/heads/:refs/remotes/upstream/
git fetch upstream
cd -
cd apps/erpnext
git config --add remote.upstream.fetch +refs/heads/:refs/remotes/upstream/
Error: None
Traceback (most recent call last):
File “/usr/local/bin/bench”, line 9, in
load_entry_point(‘bench==0.1’, ‘console_scripts’, ‘bench’)()
File “/home/erpnext/bench-repo/bench/cli.py”, line 55, in cli
bench()
File “/usr/local/lib/python2.7/dist-packages/click/core.py”, line 610, in call
return self.main(*args, **kwargs)
File “/usr/local/lib/python2.7/dist-packages/click/core.py”, line 590, in main
rv = self.invoke(ctx)
File “/usr/local/lib/python2.7/dist-packages/click/core.py”, line 936, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File “/usr/local/lib/python2.7/dist-packages/click/core.py”, line 782, in invoke
return ctx.invoke(self.callback, **ctx.params)
File “/usr/local/lib/python2.7/dist-packages/click/core.py”, line 416, in invoke
return callback(*args, **kwargs)
File “/home/erpnext/bench-repo/bench/cli.py”, line 218, in update
version_upgrade = is_version_upgrade()
File “/home/erpnext/bench-repo/bench/app.py”, line 97, in is_version_upgrade
fetch_upstream(frappe_dir)
File “/home/erpnext/bench-repo/bench/app.py”, line 123, in fetch_upstream
return exec_cmd(“git fetch upstream”, cwd=repo_dir)
File “/home/erpnext/bench-repo/bench/utils.py”, line 72, in exec_cmd
subprocess.check_call(cmd, cwd=cwd, shell=True)
File “/usr/lib/python2.7/subprocess.py”, line 540, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command ‘git fetch upstream’ returned non-zero exit status 128
erpnext@erpnext:~/frappe-bench$