Check if page parameter is null in visualforce page

Question

<c:CPPListViewComponent AccountId="{!IF(ISNULL($CurrentPage.parameters.accId), null,$CurrentPage.parameters.accId)}" RecordTypeValue="CPP"/>  

I am trying to pass the page parameters as attribute the VF component. In one of the page, the parameter is not need and I need to check if accId is null or not.

When I use the above code it works fine with the parameters. But if the parameter is not passed I get the following error

Answer 1

<c:CPPListViewComponent AccountId="{!$CurrentPage.parameters.accId}" /> 

does the same thing.

It looks like the error is inside the c:CPPListViewComponent component, since it is related to {!accId}, there is no accId in this code yet.