@Nullable
    @Override
    public Boolean isResponseStreaming(Type returnType, @Nullable MediaType produceType) {
        final Class<?> clazz = typeToClass(unwrapUnaryAsyncType(returnType));
        if (clazz == null) {
            return null;
        }

        // Non-streaming types.
        if (Maybe.class.isAssignableFrom(clazz) ||
            Single.class.isAssignableFrom(clazz) ||
            Completable.class.isAssignableFrom(clazz)) {
            return false;
        }

        if (Observable.class.isAssignableFrom(clazz)) {
            return true;
        }

        return null;
    }
Creates a new {@link ResponseConverterFunction} instance.

@param responseConverter the function which converts an object with the configured
                         {@link ResponseConverterFunction}
rxjava2/src/main/java/com/linecorp/armeria/server/rxjava2/ObservableResponseConverterFunction.java