iRule for Response Header "content-length"

Hi, I am using the irule to direct the users to the test1 pool when they send the test_string in soap data . But I also want to direct the users to test2 pool when they no any soap data sent by xml post request. My irule is the below but i am getting the "err tmm1[17512]: 01220001:3: TCL error: /Common/xml_rule - Illegal argument (line 2) invoked from within "HTTP::collect [HTTP::header Content-Length]" " error message in /var/log/ltm when no any soap data was sent. how can i regulate my irule? thanks,

when HTTP_REQUEST { HTTP::collect [HTTP::header Content-Length] } when HTTP_REQUEST_DATA { if {[findstr [HTTP::payload] "list" 1 " x" ] contains "test_string" }{

pool test1 } if {!([HTTP::header "content-length"] = 0) } { pool test2 }

HTTP::release }