If you have just changed code (for example deployed a new module or moved an existing one) read http://drupal.org/documentation/rebuild
( ! ) Fatal error: Call to a member function get() on null in /www/sevia/core/lib/Drupal.php on line 241
Call Stack
#TimeMemoryFunctionLocation
10.0023888448_drupal_exception_handler( ).../bootstrap.inc:0
20.0024895352_drupal_log_error( ).../bootstrap.inc:1933
30.0024895416drupal_maintenance_theme( ).../errors.inc:187
40.0024895816_drupal_maintenance_theme( ).../bootstrap.inc:2329
50.0025902024Drupal::config( ).../theme.maintenance.inc:57