如何判断是否找到了空XML节点？

I have XML like this:

<list>
<entry><string>...</string><string>...</string></entry>
<entry><string>...</string><string></string></entry>
<entry><string>...</string><null/></entry>
<entry><string>...</string><string>...</string><null/></entry>
</list>

How to tell that I had a <null/> element? This is the struct I'm trying to work with:

type Entry struct {
    Values []string `xml:"string"`
    Null   string   `xml:"null"`
}

OK that was embarrassing :)

type Entry struct {
    Values []string `xml:"string"`
    Nulls  []string `xml:"null"`
}