大神来帮我看一下 哪里错了

com.microsoft.sqlserver.jdbc.SQLServerException: 不能将值 NULL 插入列 'userPass'，表 'DVDground.dbo.Users'；列不允许有 Null 值。INSERT 失败。
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDatabaseError(SQLServerException.java:216)
at com.microsoft.sqlserver.jdbc.SQLServerStatement.getNextResult(SQLServerStatement.java:1515)
at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.doExecutePreparedStatement(SQLServerPreparedStatement.java:404)
at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement$PrepStmtExecCmd.doExecute(SQLServerPreparedStatement.java:350)
at com.microsoft.sqlserver.jdbc.TDSCommand.execute(IOBuffer.java:5696)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.executeCommand(SQLServerConnection.java:1715)
at com.microsoft.sqlserver.jdbc.SQLServerStatement.executeCommand(SQLServerStatement.java:180)
at com.microsoft.sqlserver.jdbc.SQLServerStatement.executeStatement(SQLServerStatement.java:155)
at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.executeUpdate(SQLServerPreparedStatement.java:314)
at com.stu.ye.DAOperation.register(DAOperation.java:29)
at com.stu.servlet.doRegister.doPost(doRegister.java:80)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)
我找不到错误在哪
他说我的插入语句出现异常 可是我反复看都没发现哪里错误了 求解答
public int register(Users user){
Connection con=null;
PreparedStatement pstmt=null;
int row=0;
//1.创建链接
try {
con=DAOConnection.conn();
//2.创建语句对象
String sql="insert into Users(userName,userPass,IDCard) values (?,?,?)";
if(con!=null){
pstmt=con.prepareStatement(sql);
//3.执行语句
pstmt.setString(1, user.getUserName());
pstmt.setString(2, user.getUserPass());
pstmt.setString(3, user.getIDCard());
row=pstmt.executeUpdate();
return row;
}else {
return 0;
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
//return 0;
}finally{
DAOConnection.close(pstmt);
DAOConnection.close(con);
}
return row;
}