Nillable SOAP headers - xsd

Question

I would like to allow some of my SOAP header elements to be nillable. This is possible for body elements, but I am not sure if it is allowed from header elements.
In the sample message below, I would like to allow the MessageDateTime to be null.
<definitions xmlns="http://schemas.xmlsoap.org/wsdl/"
xmlns:wsaw="http://www.w3.org/2006/05/addressing/wsdl"
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
xmlns:tns="http://mycompany.com/repositoryservice">
<types>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
attributeFormDefault="qualified"
elementFormDefault="qualified"
targetNamespace="http://mycompany.com/repositoryservice">
<element name="MessageDateTime" type="dateTime" />
<element name="SaveRequest">
<!-- complexType -->
</element>
</schema>
</types>
<message name="SaveRequest_Headers">
<part name="MessageDateTime" element="tns:MessageDateTime" />
</message>
<message name="SaveRequest">
<part name="parameters" element="tns:SaveRequest" />
</message>
<binding name="RepositoryServiceBinding" type="tns:IRepositoryService">
<soap:binding transport="http://schemas.xmlsoap.org/soap/http" />
<operation name="Save">
<soap:operation soapAction="http://mycompany.com/repositoryservice/Save" style="document" />
<input name="SaveRequest">
<soap:header message="tns:SaveRequest_Headers" part="MessageDateTime" use="literal" />
<soap:body use="literal" />
</input>
</operation>
</binding>
<!-- service, portType -->
</definitions>

Answer 1

It is allowed as long as the definition allows for it. In your case, all you have to do is add the nillable="true" to the element's definition. The result on .NET w/ WCF would look something like this:
[System.ServiceModel.MessageHeaderAttribute(Namespace="...")]
[System.Xml.Serialization.XmlElementAttribute(IsNullable=true)]
public System.Nullable<System.DateTime> MessageDateTime;