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 ('1c6b97a6796a93815f06626c9dae28db', -1, 1550658694, 1550658694, '345bb0fb', 75, 0, 0)

Line : 187
File : sessions.php