Issue with creation of invoice saved search

Hi All,
I am new to Suitescripting. I am creating an invoice saved search with the below condition on Invoice.
var arrInvSearchColumns = new Array();
     arrInvSearchColumns[0] = new nlobjSearchColumn('account');
     arrInvSearchColumns[1] = new nlobjSearchColumn('postingperiod');
     arrInvSearchColumns[2] = new nlobjSearchColumn('total');
         
     var arrInvSearchFilters = new Array();
     arrInvSearchFilters[0] = new nlobjSearchFilter('account', null,'is','Accounts Receivable');
            arrInvSearchFilters[0] = new nlobjSearchFilter('postingperiod', null,'is','Aug 2007');
    
     invoiceSearchResult = nlapiSearchRecord('invoice',null, arrInvSearchFilters,arrInvSearchColumns);
    
But the above code is not returning any row while there are actually plenty of invoice records for account 'Accounts Receivable', and period Aug 2007