Show Blank Values

Hi, 

I would like to ask. I'm getting problem when I use this calculation

Avg Minutes Per Refresh = AVERAGE('Refresh History'[Time Difference] )

It's hiding those rows that are blanks. But when I select the show items with no data it is showing unecessary values even it is not included in the report. I just want to show those with status " Unknown" and when unselected I want to show those with values.

I have this table: