SSRS Expression-Sum two fields

Question

I need to sum two fields but I couldn't.

Can you help me?

=iif(Fields!ABC.Value= "", Nothing, Sum(Fields!PA.Value)) 
=iif(Fields!XYZ.Value= "", Nothing, Sum(Fields!PA.Value))

It does not work that way:

=iif(Fields!ABC.Value= "", Nothing, Sum(Fields!PA.Value)) +
       iif(Fields!XYZ.Value= "", Nothing, Sum(Fields!PA.Value)) 

Answer 1

To sum them I should think you just want to default to 0 rather than Nothing

=iif(Fields!ABC.Value= "", 0, Sum(Fields!PA.Value)) +
   iif(Fields!XYZ.Value= "", 0, Sum(Fields!PA.Value)) 

Answer 2

I think what he is looking for is something like this:

=Sum(IIF(Fields!ABC.Value = "", Nothing, Fields!PA.Value)
=Sum(IIF(Fields!XYZ.Value = "", Nothing, Fields!PA.Value)