function SmartUpdate(obj, newObj, override){
  
  // frist check whether the origin object is null
  
  if(obj == null) {
  
    if(newObj == null) {
      if(override) return null;
        return obj;
    } else
        return newObj;
  }
  
  // then check whether the target object is null
  
  if(newObj == null) {
      if(override) return null;
      return obj;
  }
    
  // then do object value assign
  
  if(typeof obj === 'object' && typeof newObj === 'object'){
      
    for(var key in obj) {
      // first check all key:value pair in target obj
      
      if(newObj[key] != null) {
        if(typeof newObj[key] === 'object') obj[key] = SmartUpdate(obj[key], newObj[key]);
          else
            obj[key] = newObj[key];
      }
      else if((newObj[key] === null && newObj[key] !== undefined) || override){
        obj[key] = newObj[key];
      }  
    }
    
    for(var key in newObj) {
      // then check all key:value pair in newObj, see if there are anything to add
      // only assign the value when it is empty.
      if(obj[key] == null) obj[key] = newObj[key];
    }
    
    return obj;
    
  } else{
    
    // just going to assign the value because they are not object
    return newObj;
  }
}

Updated at Feb 26th, 2020: Even the target key-value pair is null, the function will still merge 2 objects correctly.

Example:

SmartUpdate({“a”: 1, “b”: 2, “c”: 3}, {“c”: null}) => {“a”: 1, “b”: 2, “c”: null}