OpenTelemetry计数器指标属性值显示'n.i'异常求助

我创建了一个最小可复现项目，使用Fiber启动服务器，代码如下：

package main

import (
    "context"
    "os"
    "time"

    "github.com/gofiber/contrib/fiberzap"
    "github.com/gofiber/fiber/v2"
    "github.com/gofiber/fiber/v2/middleware/favicon"
    "go.opentelemetry.io/otel"
    "go.opentelemetry.io/otel/attribute"
    "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
    "go.opentelemetry.io/otel/metric"
    sdkmetric "go.opentelemetry.io/otel/sdk/metric"
    "go.opentelemetry.io/otel/sdk/metric/metricdata"
    "go.opentelemetry.io/otel/sdk/resource"
    semconv "go.opentelemetry.io/otel/semconv/v1.18.0"
    "go.uber.org/zap"
    "go.uber.org/zap/zapcore"
)

var (
    logger *zap.Logger
)

func init() {
    var cfg zap.Config
    cfg = zap.NewDevelopmentConfig()

    // set time format
    cfg.EncoderConfig.EncodeTime = zapcore.TimeEncoderOfLayout(time.DateTime)
    // add color for console
    cfg.EncoderConfig.EncodeLevel = zapcore.CapitalColorLevelEncoder
    logger = zap.New(zapcore.NewCore(zapcore.NewConsoleEncoder(cfg.EncoderConfig), zapcore.NewMultiWriteSyncer(zapcore.AddSync(os.Stdout)), zapcore.DebugLevel))
}

func preferDeltaTemporalitySelector(kind sdkmetric.InstrumentKind) metricdata.Temporality {
    switch kind {
    case sdkmetric.InstrumentKindCounter,
        sdkmetric.InstrumentKindObservableCounter,
        sdkmetric.InstrumentKindHistogram:
        return metricdata.DeltaTemporality
    default:
        return metricdata.CumulativeTemporality
    }
}

func initProvider(ctx context.Context) func() {
    res, err := resource.New(ctx,
        resource.WithFromEnv(),
        resource.WithProcess(),
        resource.WithTelemetrySDK(),
        resource.WithHost(),
        resource.WithAttributes(
            semconv.ServiceName("server"),
            semconv.ServiceNamespace("demo"),
            semconv.ServiceVersion("0.1.0"),
        ),
    )
    if err != nil {
        logger.Fatal("failed to create resource", zap.Error(err))
    }

    otelAgentAddr, ok := os.LookupEnv("OTEL_EXPORTER_OTLP_ENDPOINT")
    if !ok {
        otelAgentAddr = "127.0.0.1:4317"
    }
    metricExp, err := otlpmetricgrpc.New(
        ctx,
        otlpmetricgrpc.WithInsecure(),
        otlpmetricgrpc.WithEndpoint(otelAgentAddr),
        otlpmetricgrpc.WithCompressor("gzip"),
        otlpmetricgrpc.WithTemporalitySelector(preferDeltaTemporalitySelector),
    )

    meterProvider := sdkmetric.NewMeterProvider(
        sdkmetric.WithResource(res),
        sdkmetric.WithReader(
            sdkmetric.NewPeriodicReader(
                metricExp,
                sdkmetric.WithInterval(2*time.Second),
            ),
        ),
    )
    otel.SetMeterProvider(meterProvider)

    return func() {
        cxt, cancel := context.WithTimeout(ctx, time.Second)
        defer cancel()
        // pushes any last exports to the receiver
        if err := meterProvider.Shutdown(cxt); err != nil {
            otel.Handle(err)
        }
    }
}

var (
    meter metric.Meter
)

func main() {
    ctx := context.Background()
    otelShutdownHook := initProvider(ctx)
    defer otelShutdownHook()

    meter = otel.Meter("demo-server")

    app := fiber.New(fiber.Config{
        AppName:           "demo-server",
        CaseSensitive:     true,
        DisableKeepalive:  true,
        EnablePrintRoutes: true,
    })
    app.Use(favicon.New())
    app.Use(fiberzap.New(fiberzap.Config{
        Logger:   logger,
        SkipURIs: []string{"/favicon.ico"},
        Fields:   []string{"time", "method", "path", "status", "respHeader:X-Request-ID", "ip", "port", "ua", "latency"},
        Levels:   []zapcore.Level{zapcore.WarnLevel},
    }))

    requestCount, _ := meter.Int64Counter(
        "demo_server/request_counts",
        metric.WithDescription("The number of requests received"),
    )

    app.Get("/hello/:app_id", func(c *fiber.Ctx) error {
        appID := c.Params("app_id")

        logger.Info("hello", zap.String("app_id", appID))

        requestCount.Add(c.UserContext(), 1, metric.WithAttributes(attribute.String("interface", "hello"), attribute.String("app_id", appID)))

        return nil
    })

    app.Get("/bye/:app_id", func(c *fiber.Ctx) error {
        appID := c.Params("app_id")

        logger.Info("bye", zap.String("app_id", appID))

        requestCount.Add(c.UserContext(), 1, metric.WithAttributes(attribute.String("interface", "bye"), attribute.String("app_id", appID)))

        return nil
    })

    app.Listen("0.0.0.0:2333")
}

发送HTTP请求：curl http://127.0.0.1:2333/hello/1024，服务器可正确获取app_id=1024，但OpenTelemetry SDK上报给OpenTelemetry Collector的属性值却显示'n.i'，恳请提供修复建议，谢谢！

内容的提问来源于stack exchange，提问作者charmer