Creation of zero invoice amount for expense report

Hello,

I have seen 2 internet expense invoices.

One expense report invoice has been created with some amount (eg. 100). This amount is equal to expense report in iexpense. Not found any issue with this transaction.

2nd expense report invoice has been created with zero amount. It is created with line type as ITEM & MISCELLANEOUS . Line type ITEM contains +ve amount and Miscellaneous contains -ve amount hence invoice amount become zero. I have not seen any -ve amount at iexpense report.

Now i would like to know when system will create with zero invoice( i.e Miscellaneous items). What is the setup.