NullPointerException 为什么会在服务器上出来?

Weblogic + ORCAL9

在BEAN中有一个方法用来检索数据,

protected Data search(String gempno, Connection conn) throws CMBusinessException ,SQLException{
.....
try{
YJC2GempBData gempBData = YJC2GempInfoComn.search(conn, gempno, null);
if ( gempBData == null ){
throw new NullPointerException();
}

} catch ( NullPointerException e ) {
throw new NullPointerException();
}catch ( Exception e ) {
throw new CMBusinessException( "" ,e );
}
}
public Data search(String gempno)throws CMBusinessException {
....
try{
if (conn_frens == null){
conn_frens = connectItfrensDB();
}
Data data = null;
data = search(gempno ,conn_frens);
} catch(SQLException e){
throw new CMBusinessException( null, e );
} catch(NamingException e){
throw new CMBusinessException( null, e );
}
}
然后在UI中来调用这个方法.
代码如下:

...........

try {
data = remoteYJ01.search(moskmData.getGEMPNO());
} catch (Exception e) {
data = null;
}
这样的话画面显示正常.但是后台里却出NullPointerException
为什么这个NullPointerException在UI里捉到了,而在EJB里还抛在后台里?