sl pull --rebase does not work when default branch is called master

[stepancheg]

$ git clone https://github.com/google/gvisor/
...

$ cd gvisor

$ sl pull
pulling from https://github.com/google/gvisor/

$ sl pull --rebase -d master
pulling from https://github.com/google/gvisor/
nothing to rebase - working directory parent is also destination

$ sl pull --rebase
abort: missing rebase destination - supply --dest / -d

Last command fails, but it works if repo default brain is "main".

[Dieken]

sl book -r 'all()' can't show branch names main and master as bookmarks, seems these two names are special.