Replace blank with specific word

kauser

Hello, 

how can i replace blank cell into specific word- 

Current output - 

F1	F2
435345	675756
56757	1232143

Expected Output

F1	F2
Debit	Credit
435345	675756
56757	1232143

Thank you 

Kauser 

alexnajm

IF [F1]=Null() OR IsEmpty([F1]) THEN "Debit" ELSE [F1] ENDIF

Then repeat again for F2!