I have a content type with a untranslated label
(see in tree application:CONTENT_KIOSQUE_LABEL)

For this content type, the XLS file is named "null.xls". It should be "application:CONTENT_KIOSQUE_LABEL.xls"

Note that into XLS file, the title is "application:CONTENT_KIOSQUE_LABEL.xls" (ok)