Compatibility with JIRA version 6.4.12

We updated Jira to the current version 6.4.12 and Xray stopped working. It was disabled and produced some exceptions in the logfile:

There was an error loading the descriptor 'Tests' of plugin 'com.xpandit.plugins.xray'. Disabling.
java.lang.RuntimeException: Unable to enable web fragment
[...]
Caused by: com.atlassian.plugin.PluginParseException: Unable to load the module's display conditions: Could not load 'com.atlassian.jira.plugin.webfragment.conditions.UserLoggedInCondition' in plugin com.xpandit.plugins.xray
[...]
Caused by: com.atlassian.plugin.web.conditions.ConditionLoadingException: Could not load 'com.atlassian.jira.plugin.webfragment.conditions.UserLoggedInCondition' in plugin com.xpandit.plugins.xray
[...]
Caused by: java.lang.IllegalStateException: Cannot create object because the plugin container is unavailable for bundle 'com.xpandit.plugins.xray'