添加的时候出错，什么原因？
[framework] 2011-10-11 11:18:49,703 - org.hibernate.util.JDBCExceptionReporter -0 [http-8080-2] WARN org.hibernate.util.JDBCExceptionReporter - SQL Error: 1364, SQLState: HY000
 [framework] 2011-10-11 11:18:49,703 - org.hibernate.util.JDBCExceptionReporter -0 [http-8080-2] ERROR org.hibernate.util.JDBCExceptionReporter - Field 'username' doesn't have a default value
 [framework] 2011-10-11 11:18:49,750 - com.hello.data.dao.impl.UserDAO -47 [http-8080-2] ERROR com.hello.data.dao.impl.UserDAO - save failed
 org.springframework.jdbc.UncategorizedSQLException: Hibernate operation: could not insert: [com.hello.data.bean.User]; uncategorized SQLException for SQL [insert into phonemanagement.userlist (passwd, companyname, flag, count, serverip) values (?, ?, ?, ?, ?)]; SQL state [HY000]; error code [1364]; Field 'username' doesn't have a default value; nested exception is java.sql.SQLException: Field 'username' doesn't have a default value
Caused by: 
java.sql.SQLException: Field 'username' doesn't have a default value
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:946)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1631)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1723)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3283)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1332)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1604)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1519)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1504)
at org.apache.commons.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:102)
at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:73)
at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:33)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2158)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2638)
at org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:48)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:250)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:298)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:181)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:107)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)
at org.springframework.orm.hibernate3.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:635)
at org.springframework.orm.hibernate3.HibernateTemplate.execute(HibernateTemplate.java:372)
at org.springframework.orm.hibernate3.HibernateTemplate.save(HibernateTemplate.java:632)
at com.hello.data.dao.impl.UserDAO.save(UserDAO.java:40)
at com.hello.model.service.impl.UserService.addUser(UserService.java:46)