title: JQuery ajax call fails when last input is filled
body: <p>JQuery noob here,</p>
  
  <p>I'm working on a simple web-app which needs to send registration info to a server.
  For some reason this code works fine when only two of the form inputs are filled in, but fails when there's information in the last one, even though I'm not using it in the code. The error callback gets called, but errorThrown is empty. My server receives no data. </p>
  
  <p>Is there anything obviously wrong with this?</p>
  
  <p>Note: the call fails when the last input is filled, no matter how many inputs are in the form.</p>
  
  <h3>JQuery:</h3>
  
  <pre><code>$(document).ready(function() {
       $("#registrationForm button.register").on("click", function(event) {
          var params = {
              email: $("#registrationForm input.email").val(),
              password: $("#registrationForm input.password").val()
          };
  
          $.ajax({
          url: "/register",
          type: "POST",
          contentType: "application/json",
          data: JSON.stringify(params),
          dataType: "json",
          success: function(data, textStatus, jqXHR) {
              console.log(data);
              if(data.user_exists==true)
              {
                  alert("Stop trying to register twice!");
              }else{
                  window.location.href = "/registered";
              }
          },
          error: function(jqXHR, textStatus, errorThrown) {
              console.error("Error:", errorThrown);
          }
      });
    });
  });
  </code></pre>
  
  <h3>And the HTML:</h3>
  
  <pre><code>&lt;form id="registrationForm"&gt;
      &lt;label&gt;Email:&lt;/label&gt;
      &lt;input name="user[email]" type="text" required="required" class="email"&gt;
      &lt;br&gt;
      &lt;label&gt;Password:&lt;/label&gt;
      &lt;input name="user[password]" type="password" required="required" class="password"&gt;
      &lt;br&gt;
      &lt;label&gt;Verify Password:&lt;/label&gt;
      &lt;input name="nothing" type="text" required="required"&gt;
      &lt;br&gt;
      &lt;button onclick="" class="btn btn-default register"&gt;Register&lt;/button&gt;
  &lt;/form&gt;
  </code></pre>