Corda RPC: A hot observable returned from an RPC was never subscribed to

[cdesch]

I'm getting the error

RPCClientProxyHandler.onRemoval - A hot observable returned from an RPC was never subscribed to. This wastes server-side resources because it was queueing observations for retrieval. It is being closed now, but please adjust your code to call .notUsed() on the observable to close it explicitly. (Java users: subscribe to it then unsubscribe). If you aren't sure where the leak is coming from, set -Dnet.corda.client.rpc.trackRpcCallSites=true on the JVM command line and you will get a stack trace with this warning.

Following this example template, and making calls with SignedTransaction result = proxy.startTrackedFlowDynamic(ExampleFlow.Initiator.class, amount,otherParty).getReturnValue().get();

This SO says that the Observable needs to be subscribed and unsubscribed to. How is that supposed to be done properly given the example?