Joomla: Warning: Missing argument 1 for CRM_Utils_System_Joomla::getDefaultSiteSettings()
The issue was reported on JIRA here: https://issues.civicrm.org/jira/browse/CRM-18411

The patch can be found here: https://github.com/civicrm/civicrm-core/pull/8164

The patch was merged in, so it is fixed in 4.7.7 onwards.