phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('a38dffdc297e9c0b34d5bbaf0f4e7f21', -1, 1540139637, 1540139637, '36e0387e', 0, 0, 0)

Line : 187
File : sessions.php