Error in SQL Update Syntax

Error in SQL Update Syntax

I am trying to update a database via an update query,but I am getting an
error that says
Error com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have
an error in your SQL syntax; check the manual that corresponds to your
MySQL server version for the right syntax to use near
'add=null,col=null,wok=null,pcol=null,pwok=null,bio=null where un ='null''
at line 1.
I have been trying for hours to figure out what the error is in my SQL
Syntax,but I haven't been able to get through.
The update query is:
query = "Update users SET em=?, mn=?,add=?,col=?,wok=?,pcol=?,pwok=?,bio=?
where un ='"+un+"'";
I need help in figuring out the error in my update syntax,Thanks.