[http.base] throw new ServletException on

According to the servlet spec, this method either throws a
ServletException if the request is not a multipart request or always
returns a collection. It never returns null. Throwing an exception seems
to be the right thing. (Karsten Ziegeler)

Signed-off-by: Stefan Bischof <stbischof@bipolis.org>

Author: stbischof

http/base/src/main/java/org/apache/felix/http/base/internal/dispatch/ServletRequestWrapper.java

@@ -384,12 +384,12 @@ public boolean isAsyncSupported()
     @Override
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public Collection<Part> getParts() throws IOException, ServletException {
-        return null;
+        throw new ServletException("No Multipart-Support available");
     }
 
     @Override
     public Part getPart(String name) throws IOException, ServletException {
-        return null;
+        throw new ServletException("No Multipart-Support available");
     }
 
     @Override