[JAVA] If you throw null to Servlet with ajax, it will be converted to blank ""

When making a request from ajax to Servlet, null was converted to blank. specification?

sampleAjax.js

  var sampleAjax = function(){

    //request
    var request = {para : null};

    //ajax communication
    $.ajax({
      type    : "GET",
      url     : "urlSample",
      data    : request,
      async   : false,
      success : function(data) {
        console.log(data);
      },
      error : function(XMLHttpRequest, textStatus, errorThrown) {
        alert("Some kind of error occurred during the request\n" + textStatus +":\n" + errorThrown);
      }
    });

  }

servlet.java

package servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet(urlPatterns={"/urlSample"})
public class SvSample extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doGet (HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

      //Parameters
      String para = req.getParameter("para");
      String para = req.getParameter("paraDummy");

      //display
      System.out.println("----");
      System.out.println(para);
      System.out.println(paraDummy);
      System.out.println("----");
    }
}

result.txt

----

null
----

Since it is blank, nothing is displayed. Parameters not in the request will be null.