Membership incompatible with XMLSitemap

Hi

I just installed Membership and it seems to be very incompatible with XMLSitemaps (XML Sitemap Generator for WordPress 4.0beta4) which is rather important nowadays.

See the error I get:
Warning: Invalid argument supplied for foreach() in /home/tapuat5/public_html/voltigers.com/wp-content/plugins/membership/membershipincludes/classes/membershippublic.php on line 1198

The XMLSitemap does work if I uninstall the membership plugin.

Could you tell me what to do ?