when processing a file association, the code calls
FA_DESCRIPTION.fetchFrom(fa),
FA_EXTENSIONS.fetchFrom(fa), and
FA_CONTENT_TYPE.fetchFrom(fa)
the fa passed in is the map of File Association parameters not the app parameters.
now FA_DESCRIPTION.fetchFrom(fa) may call APP_NAME.fetchFrom(params) to create a dummy description (if there is no description given).
now APP_NAME (if there is none) gets us into MAIN_CLASS which (if there is none) gets us to the new LAUNCHER_DATA.
All with a set of parameters not intended for anything but the FA_XXX parameters.
the result is a ConfigException in LauncherData.create(params)