Just go to Nissan/dealer and ask for the plastic cover for a 2014 DCI xtrail key, they will tell you it won't fit but its the exact same cover. It cost about a fiver.
I got one last year, tried to get it for my micra and they told me they don't do them. But it's the same key as my mums xtrail, so asked for it for that car and I was told they do it, but it won't fit. It does.