Add flag test

Author: dearchap

flag_slice_base.go

@@ -80,7 +80,7 @@ func (i *SliceBase[T, C, VC]) Serialize() string {
 // Value returns the slice of values set by this flag
 func (i *SliceBase[T, C, VC]) Value() []T {
 	if i.slice == nil {
-		return []T{}
+		return nil
 	}
 	return *i.slice
 }

flag_test.go

@@ -3036,4 +3036,9 @@ func TestSliceValuesNil(t *testing.T) {
 	assert.Equal(t, []int64(nil), NewIntSlice().Value())
 	assert.Equal(t, []uint64(nil), NewUintSlice().Value())
 	assert.Equal(t, []string(nil), NewStringSlice().Value())
+
+	assert.Equal(t, []float64(nil), (&FloatSlice{}).Value())
+	assert.Equal(t, []int64(nil), (&IntSlice{}).Value())
+	assert.Equal(t, []uint64(nil), (&UintSlice{}).Value())
+	assert.Equal(t, []string(nil), (&StringSlice{}).Value())
 }