title: Using datepicker-ui in WordPress but the value is Null everytime
body: <p>My datepicker works, at first! But if i'm checking the value of the input (with the datepicker) the value always is Null. The right value is displaying and an alert shows the right date. But in my php file i just retrieve null</p>
  
  <pre><code>&lt;form action="" method="post"&gt;
      &lt;div class="flex-grid fg-step-1"&gt;
          &lt;div class="col col-medium-6 col-small-12 "&gt;
              &lt;p style="margin-bottom: 20px;"&gt;Date Start&lt;/p&gt;
              &lt;input type="text" id="dateStart" name="dateStart" class="datepicker"&gt; 
          &lt;/div&gt;
  
          &lt;div class="col col-medium-6 col-small-12 "&gt;
              &lt;p style="margin-bottom: 20px;"&gt;Date End&lt;/p&gt;
              &lt;input type="text" id="dateEnd" name="dateEnd" class="datepicker"&gt;
          &lt;/div&gt;
  
      &lt;/div&gt;
      &lt;input type="submit" class="main_btn""&gt;
  &lt;/form&gt;
  
  </code></pre>
  
  <pre><code>jQuery(document).ready(function(){
  
      jQuery('#dateEnd').prop('disabled', true);
  
      jQuery( '#dateStart' ).datepicker({
          changeMonth: true, 
          changeYear: true,
          showAnim: "slideDown",
          dateFormat: "yy-mm-dd",
          minDate: 0,
          onSelect: function(selectedDate){
              jQuery('#dateEnd').datepicker('option', 'minDate', selectedDate);
              jQuery('#dateEnd').prop('disabled', false);
              alert(selectedDate);
          }
      });
  
      jQuery( '#dateEnd' ).datepicker({
          changeMonth: true, 
          changeYear: true,
          showAnim: "slideDown",
          dateFormat: "yy-mm-dd",
          onSelect: function(selectedDate){
              alert(selectedDate);
          }
      });
  })
  </code></pre>
  
  <pre><code>&lt;?php
  if ( $_POST['dateStart'] == Null ) {
                  $dateStart             = false;
                  $in_date_start          = "";
              } else {
                  $in_date_start = $_POST['dateStart'];
              }
  if ( $_POST['dateEnd'] == Null) {
                  $dateEnd           = false;
                  $in_date_end          = "";
              } else {
                  $in_date_end = $_POST['dateEnd'];
              }
  ?&gt;
  </code></pre>
  
  <p>The Problem is, that we are using WordPress and using our own Theme. I need a solution for retrieving the selectedDate in my php-code</p>