ibatis的问题java.sql.SQLException: Error: executeQueryForObject

ibatis的问题
java.sql.SQLException: Error: executeQueryForObject returned too many results.
at com.ibatis.sqlmap.engine.mapping.statement.MappedStatement.executeQueryForObject(MappedStatement.java:124)
at com.ibatis.sqlmap.engine.impl.SqlMapExecutorDelegate.queryForObject(SqlMapExecutorDelegate.java:518)
at com.ibatis.sqlmap.engine.impl.SqlMapExecutorDelegate.queryForObject(SqlMapExecutorDelegate.java:493)
at com.ibatis.sqlmap.engine.impl.SqlMapSessionImpl.queryForObject(SqlMapSessionImpl.java:106)
at com.ibatis.sqlmap.engine.impl.SqlMapSessionImpl.queryForObject(SqlMapSessionImpl.java:110)
at com.ibatis.sqlmap.engine.impl.SqlMapClientImpl.queryForObject(SqlMapClientImpl.java:86)
at com.cgj.dao.EmployeeDaoImpl.select(EmployeeDaoImpl.java:13)
at com.cgj.serice.ServiceImpl.selectEmployee(ServiceImpl.java:44)
at com.cgj.main.Testit.main(Testit.java:24)
Exception in thread "main" java.lang.NullPointerException
at com.cgj.main.Testit.main(Testit.java:25)
请问这是什么错误