[BUG] git pull -- error: nothing to do

After updating git from `v2.25.1` to `v2.26.0`, I've noticed that performing `git pull` on an up-to-date repository now results in a non-zero exit code and `error: nothing to do` on stderr. With version 2.25.1, `git pull` used to finish with exit code 0 and `Current branch master is up to date.` on stdout.

The current (`v2.26.0`) behaviour only happens with the following config options:
```
[pull]
    rebase = true
[rebase]
    autoSquash = true
    abbreviateCommands = true
```
If any 1 of the 3 config options is not set, there is no error.

I think, this is a bug since many scripts and utilities rely on the exit code of `git pull` and the current behaviour causes false errors.