What's the point of creating a null function and then overriding it?

question.js

//What's the point of creating a null function and then overriding it?
'use strict';
function a () {  
  var result = {};   
  result.__proto__.show = function () {
    return null;
  }   
  result.show = function (param) {  
    return foo(param);  
  }   
  return result;  
}