Problem with kv filter and empty value

Elastic Stack Logstash
1

Hi,

I'm trying to parse some syslog-ng event using grok and the kv filter.

I've this kind of log:
AMOUNT=-4,700.00\tEXCH.RATE=\tCCY=ETB\t

I use the KV filter like this :
kv {
field_split => "\t"
source => "syslogMessage"
}

when splitting with the KV, the I get EXCH.RATE with value "CCY=ETB". But I want to have EXCH.RATE with null value instead. What I'm doing wrong ?