There is a convention in .NET XML Serialization (which is used by the
webservices runtime) that allows value-types to be marked as "nil".
The convention is, for each property in a class with a name "propertyName",
if there is a companion property named "propertyNameSpecified" which is a
bool, then the propertyNameSpecified indicates whether the property of name
"propertyName" is nil or not.

See
http://msdn.microsoft.com/library/en-us/cpref/html/frlrfSystemXmlSerializationXm
lSerializerClassTopic.asp
for the doc on this.

For example, this complexType in XML Schema:
     <s:complexType name="IdType">
       <s:sequence>
         <s:element name="Name"     minOccurs="0" maxOccurs="1"
type="s:string"   nillable="true" />
         <s:element name="Stamp"    minOccurs="0" maxOccurs="1"
type="s:date"     nillable="true" />
         <s:element name="Id"       minOccurs="0" maxOccurs="1"
type="s:int"      nillable="true" />
       </s:sequence>
     </s:complexType>

will generate something like this type definition in C#:

[XmlType(Namespace="urn:myNameSpaceHere")]
public class IdType {
   [XmlElement(IsNullable=true)]  public string Name;

   [XmlElement(DataType="date")]  public System.DateTime Stamp;
   [XmlIgnore]                    public bool            StampSpecified;

   [XmlElement]    public int  Id;
   [XmlIgnore]     public bool IdSpecified;
}

---------

Notice that the string (not a value type) is marked IsNillable=true, while
the int and DateTime (both value types) are not.    In your app code, to
deal with nil values in the string, you do this:

if (instance.Name != null) ...

Conversely, to deal with nil values on value types (like the int and
DateTime), what you need to do is

if (instance.StampSpecified) ....
if (instance.IdSpecified) ....

The Id and Stamp will never actually be nil, but you treat them as nil in
app code if the flag says that they are not specified.  The same convention
applies to all value types in .NET.

--------

So, can you examine the generated files and tell me if you have the
companion  xxxSpecified  properties marked "XmlIgnore"?   If so, then you
know what to do. . .

-Dino