atomicutil: use atomicutil.Value wherever possible (#3517)

* atomicutil: use atomicutil.Value wherever possible

* fix test

* fix mux router

internal/atomicutil/value.go

@@ -17,7 +17,16 @@ func NewValue[T any](init T) *Value[T] {
 
 // Load loads the value atomically.
 func (v *Value[T]) Load() T {
-	return v.value.Load().(T)
+	var def T
+	if v == nil {
+		return def
+	}
+
+	cur := v.value.Load()
+	if cur == nil {
+		return def
+	}
+	return cur.(T)
 }
 
 // Store stores the value atomically.

internal/atomicutil/value_test.go

@@ -0,0 +1,21 @@
+package atomicutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestValue(t *testing.T) {
+	v := NewValue(5)
+	assert.Equal(t, 5, v.Load())
+
+	t.Run("nil", func(t *testing.T) {
+		var v *Value[int]
+		assert.Equal(t, 0, v.Load())
+	})
+	t.Run("default", func(t *testing.T) {
+		var v Value[int]
+		assert.Equal(t, 0, v.Load())
+	})
+}