Steps to Reproduce

Add the attached CustomUrlEncoder to zk.xml
open the attached dropupload.zul
Send a file

Current Result

onUpload event is triggered but Event.getMedia is null

Expected Result

Event.getMedia should return the media

Debug Info

dropupload.start uses zk.ajaxURI to obtain a valid /dropupload uri
If a URLEncoder adding a ?parameter=value to the default URI has been defined, the ajaxURI method will return:
/context/dropupload?parameter=value
Then, uuid, dtid and native parameters are added, which cause the url to be incorectly built as:
/context/dropupload?parameter=value?uuid=XXX&dtid=XXX& native=XXX
instead of
/context/dropupload?parameter=value&uuid=XXX&dtid=XXX& native=XXX

Root Cause

Workaround

commented in the attached zul file.