[exim] $sender_address is empty when debug

Hi.

I have just been trying to write an exim router which checks
'$sender_address' and based upon its findings it should send a duplicate
message to an extra mailbox.

I can do that. But I wondered that $sender_address is empty when debugging.

Why $sender_address is empty when debugging?
Is the debugging option insufficient?
Please teach me what is bad and how to debug this router.


My router setting is as follows.
-----------------------------------------------------------------
fw_aliases:
driver = redirect
allow_filter
condition = ${if eq{$sender_address}{test@???}}
file = /usr/local/exim/fw.from
user = exim
-----------------------------------------------------------------

and run 
# /usr/local/exim/bin/exim -bh 210.33.xx.xx -d+route+expand
-----------------------------------------------------------------
   :
   :
mail from:test@???
rcpt to:hogehoge@???
   :
   :
check verify = sender
--------> fw_aliases router <--------
local_part=test domain=example.jp
checking "condition"
expanding: $sender_address
   result:                        <------ empty!!
expanding: test@???
   result: test@???
condition: eq{$sender_address}{test@???}
   result: false
expanding: ${if eq{$sender_address}{test@???}}
   result:
fw_aliases router skipped: condition failure