Find missing onError in the project

This can be a pain to debug. Funnily enough I had an error inside the Action1<Throwable> [facepalm].

The best was to debug this is to register a global error handler. This will saw you the truth in your code:

RxJavaPlugins.getInstance().registerErrorHandler(new RxJavaErrorHandler() {
        @Override
        public void handleError(Throwable e) {
            Log.w("Error",e);
        }
});    

A discussion on github: https://github.com/ReactiveX/RxJava/issues/2293

If the onError is not implemented, then RxJava throw a OnErrorNotImplementedException exception. It's seems that RxJava didn't succed to call the onError method ("Error occurred when trying to propagate error to Observer.onError")

You can try to register an error handler to find the root exception.

static {
    RxJavaPlugins.getInstance().registerErrorHandler(new RxJavaErrorHandler() {
        @Override
        public void handleError(Throwable e) {
            e.printStackTrace();
        }
    });
}