web service with no input parameter

Question

I have a WSDL with various portTypes. Some of the contain only output

<operation name="getServerTimeZone">
  <output message="s0:getServerTimeZoneSoapOut"/>
</operation>

I would expect that the correct should be:

<operation name="getServerTimeZone">
  <input message="s0:getServerTimeZoneSoapIn"/>
  <output message="s0:getServerTimeZoneSoapOut"/>
</operation>

The problem is that when I am trying to create stubs from the WSDL using gsoap wsdl2h parser I got the following error:

No wsdl:definitions/portType/operation/input

I haven't tested with other tools (ie WSDL2Java). My question: Is it valid to have a portType with no input? I am using AltovaXML Spy and this WSDL passes the validation.... Is there any meaning having WSDL operation with no input? (I am not talking about One-Way Message Passing, where you can have input but no output - this is valid).