@Override
    @Deprecated
    public WebSocketClientBuilder rpcPreprocessor(RpcPreprocessor rpcPreprocessor) {
        return (WebSocketClientBuilder) super.rpcPreprocessor(rpcPreprocessor);
    }
Raises an {@link UnsupportedOperationException} because {@link WebSocketClient} does
not support {@link HttpPreprocessor}.

@deprecated HTTP preprocessor cannot be added to the {@link WebSocketClient}.
core/src/main/java/com/linecorp/armeria/client/websocket/WebSocketClientBuilder.java