# File lib/flowdock.rb, line 159
    def private_message(params)
      raise InvalidParameterError, "missing api_token" if blank?(@api_token)
      raise InvalidParameterError, "Message must have :content" if blank?(params[:content])
      raise InvalidParameterError, "Message must have :user_id" if blank?(params[:user_id])

      user_id = params.delete(:user_id)

      params = params.clone
      event = "message"

      post("private/#{user_id}/messages", params.merge(event: event))
    end