为什么加上这一句就出现异常？请高手看看！

<%
String name = sqlbean.toByteString(request.getParameter("name"));
String password = sqlbean.toByteString(request.getParameter("password"));
String username = sqlbean.toByteString(request.getParameter("username"));
String question = sqlbean.toByteString(request.getParameter("question"));
String answer = sqlbean.toByteString(request.getParameter("answer"));
String email = sqlbean.toByteString(request.getParameter("email"));
String mobile = sqlbean.toByteString(request.getParameter("mobile"));
String tel = sqlbean.toByteString(request.getParameter("tel"));
String depart = sqlbean.toByteString(request.getParameter("company"));
String ip = request.getRemoteAddr();
String pagesize = request.getParameter("pagesize");
String sex =sqlbean.toByteString(request.getParameter("sex"));
String Address =sqlbean.toByteString(request.getParameter("Address"));
String marriage =sqlbean.toByteString(request.getParameter("marriage"));

String sql = "select * from Usr where username='"+ username +"' or name='"+ name +"'";
sqlbean.executeQuery(sql);
if(sqlbean.next())//为什么加上这一句后就出现异常
{
out.println(。。。。。);//内容省略
}
else
{
}
去掉if(sqlbean.next())后，就正常输出，错误如下：
java.lang.NullPointerException
我测试了几次，发现错误就在if(sqlbean.next())这一句，
请高手指点，这一句改咋写？