Only show one row in pivot table if dimension is null

[rlam1234]

I have a pivot table, showing the count of items where a dimension is null. I checked the "include null values" checkbox to show this.

In the screenshot below, you can see that I am getting the count, and since the dimension is null, a dash (-) is shown.

1. How do I change the label to a value other than dash? I tried something like this:
   
   If(IsNull(my_value), 'is_null', my_value)
   
   This created a new row called "is_null", but it did not put the measure (count column) in that row. The count was still placed in the row with the dash.
   
2. Since it is a pivot table with several fields, if the first field is null, all the subsequent fields are also null. I only want to show the first level as null, and turn off the ability to expand subsequent fields. Is it possible to do that?

Any advice appreciated! Thanks.

[Saravanan_Desingh]

Did you check if it is a NULL string?

Len(my_value)=0 Or Len(Trim(my_value))=0 Or my_value=''

[rlam1234]

@Saravanan_Desingh  Thank you for your reply. I was able to figure out the first part of my question.

I have an expression where if the dimension value is null, I put in "_Unknown", instead of showing the default dash character.

My second question is this is a pivot table with several fields. Valid values are blurred out below in the screenshot, but it is working as I want. Users can expand using the + icon to see other values.

If the dimension is null, I only want to show "_Unknown" once. Is there a way to turn off the + icons so that users can't expand? Each time they expand, it will always show the same thing, so only need to show it once.