WebService dosn't work wih parameter in the method

Hi experts (Im a newbie),
I got a little problems that I cannot solve by myself... I got this simple
service:

public class StockService {

private String datiBack=null;

public String getAvailability(){
//public String getAvailability(String strType)

}

I compile it I create an .aar file I upload it in Axis2 everything works
properly I make the request thru browser
http://localhost:8080/axis2/services/StockService/getAvailability
and I got the "Sembra funzionare" wrapped in soap tag.

If I uncomment & change the getAvailability method with the one that need
a String parameter, I compile everything I upload in Axis2, same as
before, everything is ok but when I make the request
http://localhost:8080/axis2/rest/StockService/getAvailability?strType=Nylon
I got this back:

<soapenv:Fault>
<faultcode/>
<faultstring>
Required element null defined in the schema can not be found in the
request
</faultstring>
<detail/>
</soapenv:Fault>

The same problem is following the POJO example under the quickstart guide (http://ws.apache.org/axis2/1_1_1/quickstartguide.html#deploy)

So if somebody can explain me that could be great

Thanx in adavance
Ciao
Roberto