db.customers.update(
    { _id : NumberLong("1004") },
    { $unset : { first_name: "" } } 
);

connect_1    | org.bson.BsonInvalidOperationException: Document does not contain key $set
connect_1    | 	at org.bson.BsonDocument.throwIfKeyAbsent(BsonDocument.java:844)
connect_1    | 	at org.bson.BsonDocument.getDocument(BsonDocument.java:135)
connect_1    | 	at io.debezium.connector.mongodb.transforms.UnwrapFromMongoDbEnvelope.apply(UnwrapFromMongoDbEnvelope.java:82)
connect_1    | 	at org.apache.kafka.connect.runtime.TransformationChain.apply(TransformationChain.java:38)
connect_1    | 	at org.apache.kafka.connect.runtime.WorkerSinkTask.convertMessages(WorkerSinkTask.java:464)
connect_1    | 	at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:287)
connect_1    | 	at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:198)
connect_1    | 	at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:166)
connect_1    | 	at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:170)
connect_1    | 	at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:214)
connect_1    | 	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
connect_1    | 	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
connect_1    | 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
connect_1    | 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
connect_1    | 	at java.lang.Thread.run(Thread.java:748)