Gsub remplace double double ("") quotes by space

Elastic Stack Logstash
6

I had executed the following test:

 mutate { add_field => {"msg" => '""toto toto" sip:+4999999999@10.58.12.00;user=phone;tag=8b1adde9f755210b19546545b056e2c555504"'}}
 mutate { gsub => ["msg","\"\""," "] }

and got

"msg" => " toto toto\" sip:+4999999999@10.58.12.00;user=phone;tag=8b1adde9f755210b19546545b056e2c555504\"",

That looks right to me.