I'm writing XML from the following struct:

```golang
type OrderLine struct {
    LineNumber     string `xml:"LineNumber"`
    Product        string `xml:"Product"`
    Ref            string `xml:"Ref"`
    Quantity       string `xml:"Quantity"`
    Price          string `xml:"Price"`
    LineTotalGross string `xml:"LineTotalGross"`
}

```

If the `Ref` field is empty, I'd like the element to display, but be self-closing, i.e.

```
<Ref />

```

and *not*:

```
<Ref></Ref>

```

AFAIK, these two are semantically equivalent, but I would prefer a self-closing tag, as it matches the output from other systems. Is this possible?