@UnstableApi
    public ServerBuilder errorHandler(ServerErrorHandler errorHandler) {
        requireNonNull(errorHandler, "errorHandler");
        if (this.errorHandler == null) {
            this.errorHandler = errorHandler;
        } else {
            this.errorHandler = this.errorHandler.orElse(errorHandler);
        }
        return this;
    }
Adds the {@link ServerErrorHandler} that provides the error responses in case of unexpected exceptions
or protocol errors. If multiple handlers are added, the latter is composed with the former using
{@link ServerErrorHandler#orElse(ServerErrorHandler)}.

<p>Note that the {@link HttpResponseException} is not handled by the {@link ServerErrorHandler}
but the {@link HttpResponseException#httpResponse()} is sent as-is.
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java