Hi,
Try this,
IF NOT P_KUNNR IS INITIAL.
IF ( P_KUNNR NOT IN R_KUNNR[] ) OR ( R_KUNNR[] IS INITIAL ).
R_KUNNR_LINE-SIGN = 'I'.
R_KUNNR_LINE-OPTION = 'EQ'.
R_KUNNR_LINE-LOW = P_KUNNR.
APPEND R_KUNNR_LINE TO R_KUNNR.
ENDIF.
ENDIF.
Hope it helpful,
Regards,
Venkat.