Assembly: System.Xml (in System.Xml.dll)
The XML schema specification for structures allows an XML document to explicitly signal that an element's content is missing. Such an element contains the attribute xsi:nil set to true. For more information, see the World Wide Web Consortium (www.w3.org) specification, XML Schema Part 1: Structures.
If the property is set to true, the xsi:nil attribute is generated for class members that have been set to null. For example, if you set a field named MyStringArray to null, the XmlSerializer generates the following XML code.
<MyStringArray xsi:nil = "true" />
If the property is false, no XML element is generated for class members that have been set to null.
You cannot apply the property to a member typed as a value type because a value type cannot contain null. Additionally, you cannot set this property to false for value types that can be null. When such types are null, they are serialized by setting xsi:nil to true.