DB2 create table error – 104 42601 illegal symbol encountered in SQL statement

Use PowerDesigner to design the database table, put the SQL statement generated by it into DB2 for execution, and report an error: an invalid symbol was encountered in the 104 42601 SQL statement
Some SQL statements are as follows:
create table user
UserId int the not null,
The username varchar null,
Hobby varchar null,
Constraint PK_USER primary key clustered (userId)
Upon verification, it was found that the above SQL statement set the field to NULL, which cannot be written in DB2.

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