Logstash remove N/A field

I am trying to remove all the fields which have N/A next to the them like "toto: N/A", I am currently removing them with a enormous IF forest which I have hard coded but I would like a better alternative, to an enormous amount of if's, let's say I have this:

toto1: N/A
test1 {
    toto2: true
    toto3: N/A
}

I want to transform it into :

test1 {
    toto2: true
}

Can I do this with anything other then a Ruby filter? If not, how do I do it with Ruby?