Why I get an error when you run the query?

Hello! When you run an SQL query in Laravel I get an error:
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry " for key 'users_username_unique' (SQL: insert into `users` (`email`, `password`, `activationCode`, `isActive`, `updated_at`, `created_at`) values (Sokolov_A_2000@mail.ru y$KYlaTrJ4JlItR3BTQT81D.el3mt4A.Uam9DvG.6FFLKBohCaGPxQC, CMo0BXN3Dj6cM3pV, 0, 2016-06-29 13:06:38, 2016-06-29 13:06:38))
July 8th 19 at 11:11
2 answers
July 8th 19 at 11:13
You have the table there is a field users_username_unique which is superimposed a unique index.
The table already has a record with users_username_unique = "".
You perform an insert into this table without this field, this error is an attempt to create another record with users_username_unique = "".
July 8th 19 at 11:15
Attempt to create a record with a duplicate unique field `username` = "

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