code: public ModifyTerminal toNull() {
  		ModifyExpression mx = (ModifyExpression)this.astNode;
  		mx.setToNull();
  		ModifyTerminal ret = new ModifyTerminal(mx);
  		return ret;
  	}
docs: <div color='red' style="font-size:24px;color:red"><b><i>JCYPHER LANGUAGE ELEMENT</i></b></div>
  <div color='red' style="font-size:18px;color:red"><i>remove the property (set to <b>NULL</b>)</i></div>
  <br/>