title: SSRS 2012: How to get a "Select All" that returns NULL instead of an actual list of all values from a multi-select parameter?
body: <p>I have a multi-select parameter that can have a list of thousands of entries. In general, the user will pick a few entries from the list or "Select All". If they check "Select All", I would much prefer that I get a NULL or an empty string instead of a list of all values. Is there any way to do that?</p>
  
  <p>In experimenting with a work-around, I tried putting an "All" label with a null value in the list, but it is ignored (does not display in the drop-down). If I use an empty string for the value, my "All" entry does get displayed, but so does "Select All", which is confusing. Is there a way to suppress "Select All"?</p>
  
  <ul>
  <li>Mark</li>
  </ul>