Change columns in notifications nonnullable (#6764)

db/migrate/20180310000000_change_columns_in_notifications_nonnullable.rb

@@ -0,0 +1,8 @@
+class ChangeColumnsInNotificationsNonnullable < ActiveRecord::Migration[5.1]
+  def change
+    change_column_null :notifications, :activity_id, false
+    change_column_null :notifications, :activity_type, false
+    change_column_null :notifications, :account_id, false
+    change_column_null :notifications, :from_account_id, false
+  end
+end