If the export of an ODF document fails the extension will not show the correct error.
The error message

Error: unable to open file var/cache/ezodf/ootest.odt on server side

is not correct because the problem is, that the file could not be written before, because the zip binary is missing to create the file.
This should be changed to
a) disable ODF if Zip binary is missing and log the error
or
b) show a message which shows that zip binary is missing and due that ODF does not work