def is_member?(email)
      return false if self.id.nil?

      response = service.principal_list(:group_id => self.id,
        :filter_email => email,
        :filter_is_member => true)

      !response.at_xpath('//principal').nil?
    end
def is_member?(email)
      return false if self.id.nil?

      response = service.principal_list(:group_id => self.id,
        :filter_email => email,
        :filter_is_member => true)

      !response.at_xpath('//principal').nil?
    end
Public: Find the member of this group.

 email - User's email address

 Returns a boolean.