You can format the "Measure Values" and enter the desired text in the Special Values section.
In the current scenario, the hyphens are displayed even when there is a value in the cell. And this is because you have several measure values but are not displaying the measure names for every value.
If I now replace the "Metrics" dimension with the "Measure Names", the hyphens show up only when there is no value as can be seen below:
Hope this helps. Updated workbook is attached for reference.
KPI_v10.5.twbx 347.4 KB