Strange error.

[kronos]

It seems to work with Ruby 1.8.6, but doesn't work with Ruby ruby
1.9.1p129 (2009-05-12 revision 23412) [i386-darwin9]
Macintosh-2:engine kronos$ piston status vendor/plugins/restful-
authentication
fatal: Not a git repository (or any of the parent directories): .git
/opt/local/lib/ruby1.9/1.9.1/pathname.rb:967:in `glob': can't convert
Pathname into String (TypeError)
from /opt/local/lib/ruby1.9/1.9.1/pathname.rb:967:in `glob'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/lib/piston/
commands/status.rb:12:in `run'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/lib/piston/
commands/status.rb:42:in `block in start'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/lib/piston/
commands/status.rb:40:in `each'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/lib/piston/
commands/status.rb:40:in `start'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/lib/piston/
cli.rb:67:in `start'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/lib/piston/
cli.rb:121:in `<top (required)>'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/bin/piston:
5:in `require'
from /opt/local/lib/ruby1.9/gems/1.9.1/gems/piston-2.0.5/bin/piston:
5:in `<top (required)>'
from /usr/bin/piston:19:in `load'
from /usr/bin/piston:19:in `<main>'
Macintosh-2:engine kronos$ ls -la vendor/plugins/
total 0
drwxr-xr-x 4 kronos admin 136 21 июл 17:10 .
drwxr-xr-x 4 kronos admin 136 16 июл 13:33 ..
drwxr-xr-x 9 kronos admin 306 22 июл 18:45 .svn
drwxr-xr-x 16 kronos admin 544 21 июл 17:10 restful-authentication

We use svn for our project and we take the plugin from git repository.
Why does the following error occure:
"fatal: Not a git repository (or any of the parent directories): .git"
Wtf?