issue with subtracting dates and filter values as <10 or >10

[nishpowerbi]

hi,
I have 2 date columns 

some of the values in 2nd column i.e. routing approval date are null
I subtracted column 2 - column 1 
also I have 3 document types like below

for in approval when subtracted coulumn 2 - column 1 i got values 
but for in commenting doc I'm not getting values as column 2 has null values for that commenting doc

Now I want the to subtract null values from column2 - column1 such that i get some output 
eg -  0 -20 = 20

Screenshot of results im getting
1. values I get when sleected approval docs

2. no values shown for commenting docs

plz assist ne in this 
then I want to sort  the reult values as >10 and <10 

[lbendlin]

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