phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '0' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('6540f8372a6a14acdb5616c655524c1b', -1, 1540245839, 1540245839, '369c27f5', -7, 0, 0)

Line : 187
File : sessions.php