SSRS expression replace NULL with another field value

I need to write an SSRS expression to check and replace NULL field value with another field value. Can this be done?

If you have to do it a bunch of times, you can also make a reusable function to avoid a lot of typing. Here's a solution modeled off of SQL's ISNULL function:

1. Right click on the Report Document and go to Report Properties.

   

2. Navigate to the Code tab and add the following function:

   Public Function IsNull(input As Object, defaultValue As Object) As Object
     Return IIf(input Is Nothing, defaultValue, input)
   End Function
   

   

   ^{Note - Even though the custom code is expecting valid VB.NET code, you have to use the IIF Ternary operator.}

3. Then you can use it in an expression like this:

   =Code.IsNull(Fields!MyField.Value,0)