com.mongodb.MongoCommandException: Command failed with error 197

com.mongodb.MongoCommandException: Command failed with error 197: 'The field 'unique' is not valid for an _id index specification. Specification: { v: 2, key: { _id: 1 }, name: "_id_", ns: "test2.blobs", unique: true }' on server 127.0.0.1:27017. The full response is { "ok" : 0.0, "errmsg" : "The field 'unique' is not valid for an _id index specification. Specification: { v: 2, key: { _id: 1 }, name: \"_id_\", ns: \"test2.blobs\", unique: true }", "code" : 197, "codeName" : "InvalidIndexSpecificationOption" }
	at com.mongodb.connection.ProtocolHelper.getCommandFailureException(ProtocolHelper.java:75)
	at com.mongodb.connection.CommandProtocol.createCommandResult(CommandProtocol.java:140)
	at com.mongodb.connection.CommandProtocol.receiveMessage(CommandProtocol.java:131)
	at com.mongodb.connection.CommandProtocol.execute(CommandProtocol.java:84)
	at com.mongodb.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:155)
	at com.mongodb.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:219)
	at com.mongodb.connection.DefaultServerConnection.command(DefaultServerConnection.java:146)
	at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:182)
	at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:173)
	at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:145)
	at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:139)
	at com.mongodb.operation.CreateIndexesOperation$1.call(CreateIndexesOperation.java:116)
	at com.mongodb.operation.CreateIndexesOperation$1.call(CreateIndexesOperation.java:111)
	at com.mongodb.operation.OperationHelper.withConnectionSource(OperationHelper.java:186)
	at com.mongodb.operation.OperationHelper.withConnection(OperationHelper.java:177)
	at com.mongodb.operation.CreateIndexesOperation.execute(CreateIndexesOperation.java:111)
	at com.mongodb.operation.CreateIndexesOperation.execute(CreateIndexesOperation.java:66)
	at com.mongodb.Mongo.execute(Mongo.java:745)
	at com.mongodb.Mongo$2.execute(Mongo.java:728)
	at com.mongodb.DBCollection.createIndex(DBCollection.java:1492)
	at org.apache.jackrabbit.oak.plugins.document.mongo.MongoBlobStore.initBlobCollection(MongoBlobStore.java:173)
	at org.apache.jackrabbit.oak.plugins.document.mongo.MongoBlobStore.<init>(MongoBlobStore.java:74)
	at org.apache.jackrabbit.oak.plugins.document.DocumentMK$Builder.setMongoDB(DocumentMK.java:638)
	at org.apache.jackrabbit.oak.plugins.document.DocumentMK$Builder.setMongoDB(DocumentMK.java:656)