Fields splitting from kv filter not containing blank values

[Vaibhav_Gupta2 (Vaibhav Gupta)]

I am using 'kv' filter in logstash like this

kv {
source => "request"
field_split => "&?"
}

I have a message like "key=value&key1=&key2=value2"

the logstash output is coming like this

"key" : "value"
"key1" : "&key2=value2"

But it should be like this

"key" : "value"
"key1" : ""
"key2" : "value2"

Can somebody suggest how can we achieve this?

[Badger]

You could use default_keys to set the value of key1, but a kv filter parsing dynamic keys will not retain blank values.

[Vaibhav_Gupta2 (Vaibhav Gupta)]

I can not use default_keys because the real message is search query and it can be dynamic and contains any no of fields