为什么我的Go程序无法正确使用Zap日志库？

config := zap.NewDevelopmentConfig()
config.Level = zap.NewAtomicLevelAt(zap.DebugLevel)
logger, _ := config.Build()

config.EncoderConfig = zapcore.EncoderConfig{
    TimeKey:        "timestamp",
    LevelKey:       "level",
    NameKey:        "logger",
    CallerKey:      "caller",
    MessageKey:     "message",
    StacktraceKey:  "stacktrace",
    LineEnding:     zapcore.DefaultLineEnding,
    EncodeLevel:    zapcore.CapitalLevelEncoder,
    EncodeTime:     zapcore.ISO8601TimeEncoder,
    EncodeDuration: zapcore.SecondsDurationEncoder,
    EncodeCaller:   zapcore.ShortCallerEncoder,
}

config.EncoderConfig.EncodeLevel = zapcore.CapitalColorLevelEncoder

config.EncoderConfig.EncodeTime= func(w io.Writer, t time.Time, enc zapcore.PrimitiveArrayEncoder) {
    enc.AppendString(t.Format("2006-01-02 15:04:05.999999999"))
}

config.OutputPaths = []string{
    "stdout",
    "./logs/app.log",
}

config.RotationTime = time.Hour * 24
config.MaxAge = time.Hour * 24 * 7
config.MaxBackups = 7

logger, err = config.Build()

logger, err = config.Build()
if err != nil {
    panic(err)
}
defer logger.Sync()