title: jQuery validation engine, set minsize but allow empty
body: <p>I have using jQuery validation engine,</p>
  
  <p>I try to let empty text field, but validate while the field not empty</p>
  
  <p>my code is like this</p>
  
  <pre><code>&lt;input name="t_city" type="text" id="t_city" placeholder="CITY" class="validate[minSize[6]]"&gt;
  </code></pre>
  
  <p>and my javascript is like this</p>
  
  <pre><code>$("form").validationEngine({
          onValidationComplete:function(form, status){
              var city = $("input#t_city").val();
  
              if(status == true){ alert(city); }
          }
      }
  }
  </code></pre>
  
  <p>How to validate to allow if the input field is empty.?</p>