PHP Fatal error: Call to a member function save() on a non-object in registration/registration.install on line 444

drush en registration
The following extensions will be enabled: registration
Do you really want to continue? (y/n): y
class_implements(): object or string expected entity.module:461 [warning]
in_array() expects parameter 2 to be array, boolean given entity.module:461 [warning]
PHP Fatal error: Call to a member function save() on a non-object in registration/registration.install on line 415

the line is:
$registration_state->save();

if I do 'drush en registration' again, it is already enabled. I am not sure why I am getting this error when using drush