如何将对象的空属性拼接到数组中？

function appendEmptyProperties(obj) {
  var emptyProperties = [];
  
  for (var key in obj) {
    if (obj.hasOwnProperty(key) && obj[key] === null) {
      emptyProperties.push(key);
    }
  }
  
  return emptyProperties;
}

// 示例对象
var obj = {
  name: "John",
  age: null,
  gender: "Male",
  address: null
};

var emptyProps = appendEmptyProperties(obj);
console.log(emptyProps); // 输出 ["age", "address"]