What are the valid operators that can be used with nlobjSearchFilter?

Hi,

I need to write a Scheduledscript which updates certain fields in the item record if a particular field has value in it.
Can anyone let me know a way to do this?

I tried a search filtered using an operator "isnot".But I got an error saying this is an invalid operator.

  var filtersArr = new Array();   filtersArr[0] = new nlobjSearchFilter('custitem_manufacturer_text', null, 'isnot', null );    //filters[0] = new nlobjSearchFilter("quantitycommitted",null,"greaterthan",0);     var searchResultArr = nlapiSearchRecord('item', null, filtersArr, cols);

Any help is appreciated.

Thanks,
Iby