I am able to find a work around for null issue however, nmrao is there anyway by which I can add these new node as the first child of parent node? 
 
As of now it is adding the nodes as the last child nodes  -  
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns="http://www.opentravel.org/OTA/2003/05">
   <soapenv:Header/>
   <soapenv:Body>
      <OTA_HotelAvailRQ EchoToken="1234" RateRangeOnly="true" Target="Test" TimeStamp="2006-07-04T09:00:27.1343316+02:00" TransactionIdentifier="b123456789" Version="4.000" xsi:schemaLocation="http://www.opentravel.org/OTA/2003/05 OTA_HotelAvailRQ.xsd" xmlns="http://www.opentravel.org/OTA/2003/05" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
         <AvailRequestSegments> 
            <AvailRequestSegment>
               <HotelSearchCriteria>
                  <Criterion>                     
                     <RoomStayCandidates>
                        <RoomStayCandidate Quantity="1">
                           <GuestCounts>
                              <GuestCount AgeQualifyingCode="1" Count="1"/>
                           </GuestCounts>
                        </RoomStayCandidate>
						 <HotelRef ChainCode="ABC" HotelCode="03092"/>
                         <HotelRef ChainCode="ABC" HotelCode="03144"/>
                     </RoomStayCandidates>
                  </Criterion>
               </HotelSearchCriteria>
            </AvailRequestSegment>
         </AvailRequestSegments>
      </OTA_HotelAvailRQ>
   </soapenv:Body>
</soapenv:Envelope>
 
But I am trying to achieve like below otherwise I am getting an error "cvc-complex-type.2.4.a: Invalid content was found starting with element 'HotelRef'"
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns="http://www.opentravel.org/OTA/2003/05">
   <soapenv:Header/>
   <soapenv:Body>
      <OTA_HotelAvailRQ EchoToken="1234" RateRangeOnly="true" Target="Test" TimeStamp="2006-07-04T09:00:27.1343316+02:00" TransactionIdentifier="b123456789" Version="4.000" xsi:schemaLocation="http://www.opentravel.org/OTA/2003/05 OTA_HotelAvailRQ.xsd" xmlns="http://www.opentravel.org/OTA/2003/05" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
         <AvailRequestSegments> 
            <AvailRequestSegment>
               <HotelSearchCriteria>
                  <Criterion>
					<HotelRef ChainCode="ABC" HotelCode="03092"/>
                    <HotelRef ChainCode="ABC" HotelCode="03144"/>				  
                    <RoomStayCandidates>
                        <RoomStayCandidate Quantity="1">
                           <GuestCounts>
                              <GuestCount AgeQualifyingCode="1" Count="1"/>
                           </GuestCounts>
                        </RoomStayCandidate>						 
                     </RoomStayCandidates>
                  </Criterion>
               </HotelSearchCriteria>
            </AvailRequestSegment>
         </AvailRequestSegments>
      </OTA_HotelAvailRQ>
   </soapenv:Body>
</soapenv:Envelope>