Work on logstash 6.4.2 but not with 7.0.0

[heweixi]

on filter ,want to split and get a element from array
but is not work on 7.0 and work with 6.4,6.5,code like:

mutate {
split => ["message", " | "]
add_field => { "ip" => "%{message[0]}" }
}

data as:
elem1 | elem2 | elem3 | elem4

other, I also want to get array lenth and get last element

thanks very much!

[Badger]

logstash no longer supports field references like message[0], it has to be [message][0]

add_field => {
    "ip" => "%{[message][0]}"
    "last" => "%{[message][-1]}"
}