title: Split causes "Object doesn't support this property or method" exception
body: <p>call to <code>split</code> on a variable causes a <em>"Object doesn't support this property or method"</em> exception and I don't know why.
  Here's my code:</p>
  
  <pre><code>function getKontaktPersonen(kontaktSelectBox) {
     var kontaktPersonen = [];
     var id_and_name = kontaktSelectBox.attr('id');
     var id_part = getID_PartFromName(id_and_name);
     var textboxname;
     var selectboxname;
     if (kontaktSelectBox.attr('class') == 'kontaktSelectBox') {
  
          textboxname = "TextBoxKunde" + id_part;
          selectboxname = "SelectBoxKontaktPerson" + id_part;
      } else if (kontaktSelectBox.attr('class') == 'NewkontaktSelectBox') {
          textboxname = "NewTextBoxKunde" + id_part;
          selectboxname = "NewSelectBoxKontaktPerson" + id_part;
      } else {
          return false;
      }
      var kundeBox = $('#' + textboxname);
      var kundeBoxVal = kundeBox.val();
      if (kundeBoxVal != '' &amp;&amp; kundeBoxVal != null) {
       var adr_id = kundeBoxVal.split(';')[1];
        //here comes an ajax call
        //[...]
      }
  }
  </code></pre>