filter grok tag_on_failure no longer accepts false

I have a grok where I want to tag up events based on which host they're from, e.g.:

filter {
  grok {
    pattern => [ "%{SYSLOGTIMESTAMP} myservice-prod-role" ]
    add_tag => [ "myservice" ]
  }
}

However, since logstash reads log from multiple hosts that grok will
fail, but I don't want the event to be tagged as "_grokparsefailure".

And sure I can have this just after my grok:

  mutate {
    tags => [ "myservice", "_grokparsefailure" ]
    remove_tag => [ "_grokparsefailure" ]
  }

But I'd rather just write (without the mutate):

  grok {
    pattern => [ "%{SYSLOGTIMESTAMP} myservice-prod-role" ]
    add_tag => [ "myservice" ]
    tag_on_failure => false
  }

but that adds a tag called "false"... = )

According to devOpsEv on IRC this worked in 1.1.10 but changed and I
suspect it's on this commit https://github.com/logstash/logstash/commit/f0196dbdc0c9578fd51e8da193b8fe17189a160c

Not sure how to support both an array and a bool so I just did a
bugreport.

In summary:
Ideally, both tag_on_failure => false and {{tag_on_failure => [
"tagz" ]}} should work.

Br,

• Simon