title: add information to input when AJAX returns null
body: <p>When I submit a form via AJAX and it returns null, I want to append a text message below the original input box, and when I resubmit with a valid value(which means the AJAX call returns what I want), delete this message. </p>
  
  <p>How can I do this? Thank you so much!!</p>
  
  <p>I tried something like this in my AJAX call:</p>
  
  <pre><code>success: function(data){
        if(data.Status === "SUCCESS"){
                  //deal with the data
              }else{
                  //NOT SURE WHAT TO DO HERE
              }
  }
  </code></pre>