illegal argument invoked from within "http::collect ...."

I recently came across this issue when adding an iRule to mitigate log4j/spring4shell.

You may want to apply a catch statement in your secondary iRule to avoid errors:

if { $content_length > 0 } {
  if { [catch { HTTP::collect $content_length }] } {
    log local0. "data collection already in progress"
  } else {
    log local0. "collecting data 2"
  }
}