How to show credit memo amount value against invoice.

Hi Guys,

I have one report. i.e. Sales invoice report.

This report using 2 dataitems:  sales invoice header & sales invoice line.

For below exaample :  My first invoice i.e. TL586-3045-2324 we have applied a credit memo against that invoice.

I want to show on my report : For example : If  we apply a credit memo against a particular invoice, then that credit memo amount is shown on the report. i.e. negative amount is shown on report i.e.- 25640

&  if we don't apply a credit memo against a particular invoice, then that invoice amount is shown on the report i.e. 25640.

& this amount values come from customer ledger entry.

I am writing below logic on the sales invoice header- on the OnAfterGetRecord trigger.

but i didn't get right output. my output shows only positive values.

I

Is any way to do this.