updation of incident state and assignee

[suvi1]

I can able to update the Assignee Value to null, but incident state is not getting updating.

Below is the code.

  var inctkts="numberSTARTSWITHINC^active=true^stateIN2,3,6";

     var gr= new GlideRecord('incident');

  gr.addQuery('assigned_to', username1);

  gr.addEncodedQuery(inctkts);

  gr.query();

  while(gr.next()){

if (gr.getRowCount() > 0) {

gr.assigned_to='  ';

gr.state="-2";

gr.update(); 

}

       }

can any one sugguestions on the same,,

 or any other blockers to update the assignee value???