WSDL fields with min=1, Max=1, nillable,type=DateTime are seen as mandatory

<definitions name="my_api" targetNamespace="https://my_namespace" xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:tns="https://my_namespace" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap-enc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">
   <types>
      <xsd:schema targetNamespace="https://my_namespace">
         <xsd:complexType name="message">
            <xsd:all>
               <xsd:element name="message_type" type="tns:wsws_message_simple_message_type"/>
               <xsd:element name="message" type="tns:wsws_message_simple_customer_message"/>
               <xsd:element name="confirm_until" nillable="true" type="xsd:dateTime" minOccurs="1" maxOccurs="1"/>
               <xsd:element name="url" type="tns:wsws_message_simple_url"/>
            </xsd:all>
         </xsd:complexType>
...

<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="https://my_namespace">
   <SOAP-ENV:Body>
      <ns1:get_queueResponse>
         <get_queueResult>
            <messages>
               <item>
                  <message_type>queue</message_type>
                  <message/>
                  <confirm_until/>
                  <url/>
               </item>
            </messages>
         </get_queueResult>
      </ns1:get_queueResponse>
   </SOAP-ENV:Body>
</SOAP-ENV:Envelope>