Is it possible to assign a default value to web service request input parameter

I wonder if it's possible to assign a default value for web service request input parameter. Here's my input parameter in the wsdl:

<element name="pensionType" default="0" type="int">

In the code side I check for the value of pensionType like this:

if (pensionType!=0)
{ TODO code here}
else
{ return warning that no data found}

I tested this in Mozilla Poster. So from this I expected that if I didn't supply any value to pensionType I'd get that warning. I get a long error:

System.Web.Services.Protocols.SoapException: Server was unable to read request. --->  
    System.InvalidOperationException: There is an error in XML document (13, 39). ---> System.FormatException: Input string was not in a correct format.    at  
    System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) at  
    System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)    at System.Xml.XmlConvert.ToInt32(String s)  at  
    Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read44_getFileTypesRequest(Boolean isNullable, Boolean checkType)    at  
    Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read45_getFileTypes(Boolean isNullable, Boolean checkType)    at  
    Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read62_getFileTypes() at  
    Microsoft.Xml.Serialization.GeneratedAssembly.ArrayOfObjectSerializer24.Deserialize(XmlSerializationReader reader)    at  
    System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events) 
--- End of inner exception stack trace ---    at  
    System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)   at  
    System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle)    at  
    System.Web.Services.Protocols.SoapServerProtocol.ReadParameters()   
--- End of inner exception stack trace ---    at  
    System.Web.Services.Protocols.SoapServerProtocol.ReadParameters() at  
    System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest(

You can do like this:

if(pensionType != null)
{
    if (pensionType!=0)
    { TODO code here}
    else
    { return warning that no data found}
}

This may help you..!!