func Sort(mapValue reflect.Value) SortedMap {
	if mapValue.Type().Kind() != reflect.Map {
		return nil
	}
	// Note: this code is arranged to not panic even in the presence
	// of a concurrent map update. The runtime is responsible for
	// yelling loudly if that happens. See issue 33275.
	n := mapValue.Len()
	sorted := make(SortedMap, 0, n)
	iter := mapValue.MapRange()
	for iter.Next() {

	activation := &testActivation{variables: variablesMap}

	// add foo as a string
	variablesType.Fields["foo"] = apiservercel.NewDeclField("foo", apiservercel.StringType, true, nil, nil)
	variablesMap.Append("foo", func(_ *MapValue) ref.Val {
		return types.String("foo-string")
	})

	exp := "variables.foo == 'foo-string'"
	v, err := compileAndRun(env, activation, exp)
	if err != nil {
		t.Fatalf("%q: %v", exp, err)
	}