Confluent Cloud with MongoDB sink connect is not working

I'm trying to connectting confluent kafka connect with mongodb sink,but its not working as expected, it throws null pointer exception.

My confluent development environment are running in GCP VM instance.

And installed "confluent-hub install mongodb/kafka-connect-mongodb:latest"

Below are my sink configuration.

{
 "name": "today-menu-sink",
 "config": {    
      "connector.class":"com.mongodb.kafka.connect.MongoSinkConnector",
      "tasks.max":"1",
      "topics":"newuser",
      "connection.uri":"mongodb+srv://*********************.mongodb.net",
      "database":"BigBoxStore",
      "collection":"users",
      "key.converter":"org.apache.kafka.connect.json.JsonConverter",
      "key.converter.schemas.enable":false,
      "value.converter":"io.confluent.connect.avro.AvroConverter",
      "value.converter.schema.registry.url" : "http://*******:8081" ,
      "value.converter.schemas.enable":true
      }
}