Cannot set "quote_char" as nil

[whirlwind110]

My logstash.conf:
input {
file {
path => ["/root/dx.txt"]
start_position => "beginning"
codec => csv {
quote_char => nil
}
}
}
All of quote_char => nil , quote_char => "nil" and quote_char => "" will throw an error is exception=>ArgumentError, :message=>":quote_char has to be nil or a single character String"

[whirlwind110]

quote_char => "\x00" works, it is better to be specified in the Docs.