Somehow, the following is the output of:

hg branches -C
00 00 00 00 00 00 00 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 35 33 39 30 3A
(in HEX).

The NULs at the beginning cause fisheye to think that a branch-name exists, however later this gets .trim()med and is therefore empty.

FishEye should skip any branch it encounters without a name.