title: Nillable SOAP headers
body: <p>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.</p>
  
  <p>In the sample message below, I would like to allow the MessageDateTime to be null.</p>
  
  <pre><code>&lt;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"&gt;
    &lt;types&gt;
      &lt;schema xmlns="http://www.w3.org/2001/XMLSchema"
              attributeFormDefault="qualified"
              elementFormDefault="qualified"
              targetNamespace="http://mycompany.com/repositoryservice"&gt;
        &lt;element name="MessageDateTime" type="dateTime" /&gt;
        &lt;element name="SaveRequest"&gt;
          &lt;!-- complexType --&gt;
        &lt;/element&gt;
      &lt;/schema&gt;
    &lt;/types&gt;
    &lt;message name="SaveRequest_Headers"&gt;
      &lt;part name="MessageDateTime" element="tns:MessageDateTime" /&gt;
    &lt;/message&gt;
    &lt;message name="SaveRequest"&gt;
      &lt;part name="parameters" element="tns:SaveRequest" /&gt;
    &lt;/message&gt;
    &lt;binding name="RepositoryServiceBinding" type="tns:IRepositoryService"&gt;
      &lt;soap:binding transport="http://schemas.xmlsoap.org/soap/http" /&gt;
      &lt;operation name="Save"&gt;
        &lt;soap:operation soapAction="http://mycompany.com/repositoryservice/Save" style="document" /&gt;
        &lt;input name="SaveRequest"&gt;
          &lt;soap:header message="tns:SaveRequest_Headers" part="MessageDateTime" use="literal" /&gt;
          &lt;soap:body use="literal" /&gt;
        &lt;/input&gt;
      &lt;/operation&gt;
    &lt;/binding&gt;
    &lt;!-- service, portType --&gt;
  &lt;/definitions&gt;
  </code></pre>