config parsing error

[nix8]

If you use { in if condition the bitfan stuck on start.

example:
filter {
if "message" =~ "^{" {
#if "{" in [message] { -> this one doesn't help
...
}
}

workaround:
filter {
eval {
expressions => { "msg_is_json" => "( [message] =~ '^{' ) ? true : false" }
}
if [msg_is_json] {
...
}
}