[CMT8.4.1.1209]When assign the target column, it will add not null attribute default.

1There are two tables:
Create table cmt(a int, b int);
insert into cmt values(1,1),(2,2),(3,3)
Create table cmt1(a char(1), c int);
insert into cmt1 values('a',1),('2',2),('3',3)

2 Do migration from online to online
Goto step3, change cmt target table to cmt1, input the target column of b.

3 Double click column b of table cmt in left tree.

Actual result:
The nullable attribute hasn't been choosed.