Testing for (blank) formula result -- different from ISBLANK() -- missing in Power Pivot data model

Ouput from Power Pivot pivot table is giving the cell value (blank).  I'd like to test for this result.  However, for example, ISBLANK(+P4) returns FALSE, and of course so does ISBLANK(+O4).

How could I flag that the (blank) cell has been created in my pivot table (using power pivot Excel 2019)? 

The blanks come from a data model with a relationship between two tables when there are legitimate blanks (no data) in the keys used to join the tables.

Thanks