public VirtualHostBuilder errorHandler(ServiceErrorHandler errorHandler) {
        requireNonNull(errorHandler, "errorHandler");
        if (this.errorHandler == null) {
            this.errorHandler = errorHandler;
        } else {
            this.errorHandler = this.errorHandler.orElse(errorHandler);
        }
        return this;
    }
Adds the {@link ServiceErrorHandler} that handles exceptions thrown in this virtual host.
If multiple handlers are added, the latter is composed with the former using
{@link ServiceErrorHandler#orElse(ServiceErrorHandler)}.
core/src/main/java/com/linecorp/armeria/server/VirtualHostBuilder.java