ContentType configuration is not valid

[ChenZheOnePiece]

I config contentType: application/json but not available

spring:
  cloud:
    stream:
      default:
        contentType: application/json
      function:
        definition: sendEmail;receiveEmail;sendMsg;receiveMsg
      bindings:
        sendEmail-out-0:
          destination: email
        receiveEmail-in-0:
          destination: email
        sendMsg-out-0:
          destination: msg
        receiveMsg-in-0:
          destination: msg

this is my log I want kown when I config contentType: application/json ,json string can automatic cast to java bean , Or what I should do.

MessageProperties [headers={}, timestamp=Wed Dec 04 16:41:55 CST 2019, messageId=17b78960-e69d-e4ad-fd79-629ce8c7a013, contentType=text/plain, contentEncoding=UTF-8, contentLength=0, receivedDeliveryMode=PERSISTENT, priority=0, redelivered=false, receivedExchange=msg, receivedRoutingKey=msg, deliveryTag=1, consumerTag=amq.ctag-hhiJVa-1Y0QfVMrNIk23jg, consumerQueue=msg.anonymous.NTtI77o2RJmq3LVBr32Q0g]), contentType=text/plain, timestamp=1575448915141}]

[sabbyanandan]

This doesn't directly apply to samples in this repo. For questions like this, please use StackOverflow.