Object Data Source With Reporting Services In Visual Studio?

I'm working on a site where we want to include a pie chart on a page. Right now I'm working on implementing that through Reporting Services (RDLC file) with an object data source.The SelectMethod of my object data source is a method that returns a list of business objects; lets say a List<Alpha> and Alpha has a sub object Beta with a Name property. In my report definition I have set the Category groups to be: =Fields!Beta.Value.Name this means that Alpha.Beta.Name are my pie slices. I got the following error:

An error has occurred during report processing. The Group expression for the rouping 'chart1_CategoryGroup1' contains an error: Object variable or With block variable not set.I was able to confirm this is because Beta is nullable and was able to fix the issue by updating the object Alpha to return a new Beta() if the Beta property is null. This solution is not ideal though because there are other places in my code where I need Beta to be null if it doesn't have a value yet.Is there a way to update the report definition to accept a null property as valid? Ideally I would like to specify the value as "Not Set" if Beta is null.