Calling 'drush gent' results in errors rather than drush messages

webchicks-MacBook-Pro:modules webchick$ drush gent
WD php: Warning: Missing argument 1 for drush_devel_generate_terms() [warning]
in drush_devel_generate_terms() (line 97 of
/Users/webchick/Sites/core/sites/all/modules/devel/devel_generate/devel_generate.drush.inc).
Invalid vocabulary name:                                             [error]
Missing argument 1 for drush_devel_generate_terms() in               [warning]
drush_devel_generate_terms() (line 97 of
/Users/webchick/Sites/core/sites/all/modules/devel/devel_generate/devel_generate.drush.inc).
An error occurred at function : drush_devel_generate_terms           [error]

Seems like Drush could be a bit more graceful here.

See also #950988: drush gen* gives confusing feedback.