Just for the record, you might notice here that there are 3 states a field can have (in VFP), two of those states used to exist in FPDos:
Blank - Hasn't been filled in yet (use ISBLANK() to check)
Null - Is marked as having No data (use ISNULL() to check)
Something - May be spaces, or whatever values are valid for the field's data type. You can see if it's spaces/tabs using EMPTY()
So:
ISNULL( .NULL. ) = .T.
ISBLANK( .NULL. ) = .F.
EMPTY( .NULL. ) = .F.
Tbl.Fld is a "blank" field:
ISNULL( tbl.Fld ) = .F.
ISBLANK( tbl.Fld ) = .T.
EMPTY( tbl.Fld ) = .T.
Tbl.Fld = 0 or spaces:
ISNULL( tbl.Fld ) = .F.
ISBLANK( tbl.Fld ) = .F.
EMPTY( tbl.Fld ) = .T.
Tbl.Fld <>0 or has some characters:
ISNULL( tbl.Fld ) = .F.
ISBLANK( tbl.Fld ) = .F.
EMPTY( tbl.Fld ) = .F.