此处错误输出，https://github.com/Marium36/blog/blob/master/errors
GitHub代码https://github.com/Marium36/blog/
我正在关注Ruby On Rails在线课程。
到目前为止，我已经能够按照说明创建User的Scaffold，并将两个字段添加到预先存在的表Post和Comments
rails g scaffold User first_name:string last_name:string
rails g migration AddUseridToPosts user:references
rails g migration AddUseridToComments user:references
当我尝试运行rake db:migrate时，我发现了很多错误，充满了多页内容。
可能出什么问题了？？？
这是error
的开头ruby@ruby-VirtualBox:~/blog$ rake db:migrate --trace
** Invoke db:migrate (first_time)
** Invoke db:load_config (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:load_config
** Execute db:migrate
== 20190621201248 AddUseridToPosts: migrating =================================
-- add_reference(:posts, :user, {:null=>false, :foreign_key=>true})
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
SQLite3::SQLException: Cannot add a NOT NULL column with default value NULL
/home/ruby/.rvm/gems/ruby-2.6.3/gems/sqlite3-1.4.1/lib/sqlite3/database.rb:147:in `initialize'
/home/ruby/.rvm/gems/ruby-2.6.3/gems/sqlite3-1.4.1/lib/sqlite3/database.rb:147:in `new'
/home/ruby/.rvm/gems/ruby-2.6.3/gems/sqlite3-1.4.1/lib/sqlite3/database.rb:147:in `prepare'
/home/ruby/.rvm/gems/ruby-2.6.3/gems/sqlite3-1.4.1/lib/sqlite3/database.rb:193:in `execute'