static UnframedGrpcStatusMappingFunction withDefault(
            UnframedGrpcStatusMappingFunction statusMappingFunction) {

        requireNonNull(statusMappingFunction, "statusMappingFunction");
        if (statusMappingFunction == UnframedGrpcStatusMappingFunction.of()) {
            return statusMappingFunction;
        }
        return statusMappingFunction.orElse(UnframedGrpcStatusMappingFunction.of());
    }
Ensure that unframedGrpcStatusMappingFunction never returns null by falling back to the default.
grpc/src/main/java/com/linecorp/armeria/server/grpc/UnframedGrpcErrorHandlerUtil.java