Rails 3: Why am I getting EOFError with DELETE request and no form body?

I created the following route in Rails 3:

delete '/api/v1/foo/groups/:group_id', to: 'Manager#delete_group', constraints: { group_id: /\d+/ }

I am using Postman to send a DELETE request to that route without a form body. Why am I getting the following error?

EOFError in ManagerController#delete_group
bad content body

When I add dummy values to the form body then I don't get an error.