In the context of data selection I'm seeing Data Selection <Null> map to ' ' (that's a space) and <Blank> map to SPACE. For example when testing TQEDSP for blank or NULL in a custom table F5531ATQ with prefix TQ:
Where | EDI - Successfully Processed (F5531ATQ)(EDSP)[BC] | is equal to | <Blank>
Or | EDI - Successfully Processed (F5531ATQ)(EDSP)[BC] | is equal to | <Null>
Is generating this SQL in the debug log:
SELECT * FROM TESTDTA92/F5531ATQ WHERE ( ( TQEDSP = SPACE OR TQEDSP = ' ' ) ) ORDER BY TQYLNO ASC,TQLITM ASC
It seems to be expecting that NULL has been normalized to a space. I am not sure about the difference between SPACE and ' ', but when I want to reproduce a logged query that says SPACE, I put ' ' and it gets the same result so they seem functionally equivalent.
JDE 9.2 on IBM i 7.2, using DB2 for i.