after adding fields on KNA1 using append structure, not null dn't work

Hello, all.

let me ask you something.

after adding fields on standard table 'KNA1' using append structure, not null , default value doesn't work.

when I check table using data object check(utilities > data object > check), the report says like this.

Fld name Position Data Type Length Decimals Not null Default

MANDT 1 VARCHAR2 9 X '000'

KUNNR 2 VARCHAR2 30 X ' '

LAND1 3 VARCHAR2 9 X ' '

ZMBRN 178 VARCHAR2 30 X ' '

ZKUNNR 179 VARCHAR2 30

ZSEQ 180 VARCHAR2 12

fields ZKUNNR, ZSEQ doesn't check not null, default.

Any advice will help.

thank in advance.