Compiling Widget Set with Ant

Vaadin 6 / 7 / 8
1

Hi,
I am building an Ant script to generate and compile a widget set. The script is based on an example that came with Vaadin 6.
The widget set module file (*.gwt.xml) seems to be generated correctly and the gwt compiler will compile it without problems (for all 6 browser permutations).
When I manually edit the module file and uncomment the line


    <!--  <set-property name="user.agent" value="gecko1_8"/>  -->

to speed up compilation, the compiler fails with the following error


     [java]
 Loading inherited module 'helloworld'
     [java]
    [ERROR]
 Property 'user.agent' not found
     [java]
    [ERROR]
 Failure while parsing XML
     [java]
 com.google.gwt.core.ext.UnableToCompleteException: (see previous log entries)
     [java]
 	at com.google.gwt.dev.cfg.ModuleDefSchema$PropertyAttrCvt.convertToArg(ModuleDefSchema.java:1088)
     [java]
 	at com.google.gwt.dev.util.xml.HandlerArgs.convertToArg(HandlerArgs.java:64)
     [java]
 	at com.google.gwt.dev.util.xml.HandlerMethod.invokeBegin(HandlerMethod.java:221)
     [java]
 	at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.startElement(ReflectiveParser.java:294)
...

Any idea what I am missing here?

Rüdiger