API validation is bypassed if content-type header is missing

Hi everyone, I think we have found a bug in restates's API validation.

Given a service with 3 mandatory arguments make(str),year(str),model (int), we found that this request

curl --request POST \
  --url 'http://restate:8080/Vins/notify_missing_suggested_vin/send' \
  --header 'Content-Type: application/json'

fails with 400 status error and this message

{"message":"input validation error: Empty body not allowed"}

while this

curl --request POST \
  --url 'http://restate:8080/Vins/notify_missing_suggested_vin/send'

succeeds, and creates an invocation with broken parameters

{"invocationId":"inv_1faXAMNrjkWq46yXz5nAKyjfuVEOa2rI7n","executionTime":"2025-05-29T02:20:35.027000000Z","status":"Accepted"}

which results in a never ending failing invocation since those empty parameters were actually expected.

Please let me know if you think we made a mistake filing this. Thanks for creating restate it is awesome.