db/seeds.rb　にダミーデータを作成しようとするとエラーが発生しました（＞＜）

現在、usersテーブルに100件のダミーデータを追加使用したいと思い
下記コードを実行してみました

場所：db/seeds.rb

100.times do |n|
  email = Faker::Internet.email
  password = "password"
  User.create!(email: email,
               password: password,
               password_confirmation: password,
               )
end

こちらにを実行すると下記がエラーとして帰ってきました
エラーの内容が↓です

ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint

なのでこちらを元に調べるとにた様な説明もありましたが、？？？です
全てパスワードが同じなどが問題なのでしょうか・・・？
すでに一部データがあるのでダブりの為×となっているのでしょうか？
有識者の方々、なぜダミーデータを作ろうとするとエラーがでるか
ヒントでいいので頂く事は可能でしょうか・・・？（＞＜）

http://stackoverflow.com/questions/39512689/pguniqueviolation-error-duplicate-key-value-violates-unique-constraint

↓がエラーの内容です
何卒、何卒、何卒、ご意見をいただければ幸いです。

vagrant@vagrant-ubuntu-trusty:~/workspace/achieve$ rake db:seed
rake aborted!
ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_users_on_uid_and_provider"
DETAIL:  Key (uid, provider)=(, ) already exists.
: INSERT INTO "users" ("email", "encrypted_password", "created_at", "updated_at", "confirmation_token", "confirmation_sent_at") VALUES ($1, $2, $3, $4, $5, $6) RETURNING "id"
/home/vagrant/workspace/achieve/db/seeds.rb:4:in `block in <top (required)>'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `times'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `<top (required)>'
PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_users_on_uid_and_provider"
DETAIL:  Key (uid, provider)=(, ) already exists.
/home/vagrant/workspace/achieve/db/seeds.rb:4:in `block in <top (required)>'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `times'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `<top (required)>'
Tasks: TOP => db:seed
(See full trace by running task with --trace)
vagrant@vagrant-ubuntu-trusty:~/workspace/achieve$
vagrant@vagrant-ubuntu-trusty:~/workspace/achieve$ rake db:seed
rake aborted!
ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_users_on_uid_and_provider"
DETAIL:  Key (uid, provider)=(, ) already exists.
: INSERT INTO "users" ("email", "encrypted_password", "created_at", "updated_at", "confirmation_token", "confirmation_sent_at") VALUES ($1, $2, $3, $4, $5, $6) RETURNING "id"
/home/vagrant/workspace/achieve/db/seeds.rb:4:in `block in <top (required)>'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `times'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `<top (required)>'
PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_users_on_uid_and_provider"
DETAIL:  Key (uid, provider)=(, ) already exists.
/home/vagrant/workspace/achieve/db/seeds.rb:4:in `block in <top (required)>'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `times'
/home/vagrant/workspace/achieve/db/seeds.rb:1:in `<top (required)>'
Tasks: TOP => db:seed
(See full trace by running task with --trace)
vagrant@vagrant-ubuntu-trusty:~/workspace/achieve$