Magento – How to set filter in a SOAP request where the SOAP Client is implemented in Plain JAVA

Before i ask the question, let me just put it this way that i have found couple of close answers to my question. But these answers are fit for the clients implemented in PHP on a server (things are a bit easier this way)

But I am using the latest set of SOAP API's to connect to Magento from an Android client written in Java. I have a set of requirements where i have to filter the products, orders by various parameters.

Unfortunately I am not able to set the filters correctly.
Below is a snippet of the SOAP request I am making in one of the cases (the error response i have posted below it).

Please help me in configuring the correct filter.

<soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:Magento" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/">
   <soapenv:Header/>
   <soapenv:Body>
      <urn:catalogProductList soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
         <sessionId xsi:type="xsd:string">d983bbee001cff69e25fdc75b5ad3394</sessionId>
         <filters xsi:type="urn:filters">
            <!--You may enter the following 2 items in any order-->
            <!--Optional:-->
            <filter xsi:type="urn:associativeArray" soapenc:arrayType="urn:associativeEntity[]">
                **<key xsi:type="xsd:string">product_id</key>
                <value xsi:type="xsd:string">2</value>**
        </filter>
            <!--Optional:-->
            <complex_filter xsi:type="urn:complexFilterArray" soapenc:arrayType="urn:complexFilter[]">
            </complex_filter>
         </filters>
         <storeView xsi:type="xsd:string">malaysian</storeView>
      </urn:catalogProductList>
   </soapenv:Body>
</soapenv:Envelope>

Response —

<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
   <SOAP-ENV:Body>
      <SOAP-ENV:Fault>
         <faultcode>SOAP-ENV:Server</faultcode>
         <faultstring>Call to a member function getAttributeCode() on a non-object</faultstring>
      </SOAP-ENV:Fault>
   </SOAP-ENV:Body>
</SOAP-ENV:Envelope>