def remove_credential(username)
      raise ArgumentError, "The username cannot be nil"   unless username
      raise ArgumentError, "The username cannot be empty" if username.empty?

      self.service.removeCredential(username.to_s)
      
      @credentials = nil
    end
def remove_credential(username)
      raise ArgumentError, "The username cannot be nil"   unless username
      raise ArgumentError, "The username cannot be empty" if username.empty?

      self.service.removeCredential(username.to_s)
      
      @credentials = nil
    end
Remove an existing network storage credential specified by the username from the network storage instance