Make user.email nullable in the db

db/migrate/20151019133719_remove_user_constraints.rb

@@ -0,0 +1,5 @@
+class RemoveUserConstraints < ActiveRecord::Migration
+  def change
+    change_column(:users, :email, :string, null: true, unique: true)
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20151016110703) do
+ActiveRecord::Schema.define(version: 20151019133719) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -267,7 +267,7 @@ ActiveRecord::Schema.define(version: 20151016110703) do
   add_index "tags", ["proposals_count"], name: "index_tags_on_proposals_count", using: :btree
 
   create_table "users", force: :cascade do |t|
-    t.string   "email",                                default: "",    null: false
+    t.string   "email",                                default: ""
     t.string   "encrypted_password",                   default: "",    null: false
     t.string   "reset_password_token"
     t.datetime "reset_password_sent_at"