PHP warnings during uninstallation

uninstalling the module throws two PHP warnings.

drush @d6 pm-uninstall environment_indicator
The following modules will be uninstalled: environment_indicator
Do you really want to continue? (y/n): y
WD php: Missing argument 1 for environment_indicator_uninstall() in  [error]
/mnt/hgfs/projects/d6/htdocs/sites/all/modules/environment_indicator/environment_indicator.install
on line 13.
WD php: Missing argument 2 for environment_indicator_uninstall() in  [error]
/mnt/hgfs/projects/d6/htdocs/sites/all/modules/environment_indicator/environment_indicator.install
on line 13.
environment_indicator was successfully uninstalled.                  [ok]