public generatedClassResponse search (string p1, long p2);

public class searchRequest {
   //omitted non param const

    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "4.0.0.0")]
    [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Advanced)]
    [System.ServiceModel.MessageContractAttribute(WrapperName="searchEvents", WrapperNamespace="http://test.com/", IsWrapped=true)]

    public searchRequest (string p1, long? p2) { //p2 type modified
        [System.ServiceModel.MessageBodyMemberAttribute(Namespace="http://test.com/", Order=0)]
        [System.Xml.Serialization.XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified)]
        public string P1

        [System.ServiceModel.MessageBodyMemberAttribute(Namespace="http://test.com/", Order=0)]
        [System.Xml.Serialization.XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified)]
        public long2? P2
   }
}

<search>
    <P1>blah</P1>
    <P2 xsi:nill="true"></P2>
</search>