unique tag panic on slice contains nil elem

[Wanghb1]

i want to make sure elem of pointer slice is not nil，meanwhile, i also need the Name field is unique.

the former can be achieved like:

struct {
F1 []*A validate:"dive,required"
}

however, the unique tag on nil elem cause panic

func TestName(t *testing.T) {
type A struct {
Name string
}
e := struct {
F1 []*A validate:"unique=Name"
}{F1: []*A{nil}}
err := validate.Struct(e)
assert.Error(t, err)
}

it turns out:
panic: reflect: call of reflect.Value.FieldByName on zero Value [recovered]
panic: reflect: call of reflect.Value.FieldByName on zero Value