serialize empty element

I've created a class, but when I serialize it I want the empty properties to
generate elements who's properties haven't been set.

What's happening:
<Identity>
<BirthDate>0000 1-01-01T00:00:00.000 00000-08:00</BirthDate>
</Identity>

What i want:
<Identity>
<BirthDate>0000 1-01-01T00:00:00.000 00000-08:00</BirthDate>
<Gender/>
</Identity>

This is my class:

[Serializable]
[System.Xml.Seri alization.XmlTy peAttribute(Nam espace="http://test")]
[System.Xml.Seri alization.XmlRo otAttribute(Nam espace="http://test",
IsNullable=fals e)]
public class Identity
{
/// <remarks/>
[System.Xml.Seri alization.XmlEl ementAttribute( Form=System.Xml .Schema.XmlSche maForm.Unqualif ied)] public System.DateTime BirthDate; /// <remarks/[System.Xml.Seri alization.XmlEl ementAttribute( Form=System.Xml .Schema.XmlSche maForm.Unqualif ied)] public string Gender;}