how to configure a proxy radius server but the username doesn't have any realm ?

[freddychu]

Hi,
   I want to configure a proxy radius server and the username doesn't have
any realm, just like 'tom'.
   So I configure realm NULL section in proxy.conf file, but it doesn't
work, the error message in radiusd terminal when redius server received the
accounting message: 
   Proxying request 0 to home server 218.83.175.155 port 1813
   The message can't be proxy to myProxyPool_1, I don't understand why the
home server become 218.83.175.155. 
Can anybody help me? How to configure it ?

proxy.conf file: 
#home server 1
home_server myProxyServer_1 {
    type = auth+acct
    ipaddr = 192.168.1.111  
    port = 1812
    secret = testing123   
    require_message_authenticator = no
    response_window = 20
    zombie_period = 40
    revive_interval = 120
    status_check = status-server
    check_interval = 10
    num_answers_to_alive = 3
    coa {
        irt = 2
        mrt = 16
        mrc = 5
        mrd = 30
    }
}
#home server 2
home_server myProxyServer_2 {
    type = auth+acct
    virtual_server = localserver
}
# home server pool 1
home_server_pool myProxyPool_1{
    type = fail-over
    home_server = myProxyServer_1
    home_server = myProxyServer_2
}
#realm
realm chuanwei.com {
    auth_pool = myProxyPool_1
    acct_pool = myProxyPool_1
    nostrip
}
realm NULL {
       authhost        = myProxyPool_1
       accthost        = myProxyPool_1
       secret          = testing123
}

Freddy