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 ('a5bccbd5b9249e98e7ce4cb255bea4db', -1, 1539723259, 1539723259, '36e11a2c', 15, 0, 0)

Line : 187
File : sessions.php