I am trying to serialize a class several of the data-members are Nullable objects, here is a example

[XmlAttribute("AccountExpirationDate")]
public Nullable<DateTime> AccountExpirationDate 
{ 
  get { return userPrincipal.AccountExpirationDate; } 
  set { userPrincipal.AccountExpirationDate = value; } 
}

However at runtime I get the error

Cannot serialize member 'AccountExpirationDate' of type System.Nullable`1[System.DateTime]. XmlAttribute/XmlText cannot be used to encode complex types.

However I checked and Nullable is a SerializableAttribute. What am I doing wrong?

c# xml-serialization nullable
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