Why my SmarFIlter request is /null?

I've just started using SapUI, and I'm trying to use SmartFilter, but all my querys go like:

http://xxxxxxxxxxxxx/sap/opu/odata/sap/ZPGW_QUOTATION_SRV/null?$skip=0&$top=10&$filter=startswith(undefined,22)&$inlinecount=allpage

XML

<smartFilterBar:SmartFilterBar id="smartFilterBar"
entityType="RfcSearchRequisitions">
</smartFilterBar:SmartFilterBar>