我刚刚将我的应用程序从Rails 4.2.7升级到Rails 5.0.0.1。我使用RailsDiff来确保我已经覆盖了所有内容，我相信我做到了。到目前为止，一切都很顺利，直到我的应用程序加载。
现在我看到了这个错误：

Sprockets::ArgumentError at /
require_tree argument must be a directory

这是我的application.css：

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
 * or any plugin's vendor/assets/stylesheets directory can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope. *
 *= require_tree .
 *= require_self
 */

这是我的application.js

// This is a manifest file that'll be compiled into application.js, which will include all the files
// listed below.
//
// Any JavaScript/Coffee file within this directory, lib/assets/javascripts, vendor/assets/javascripts,
// or any plugin's vendor/assets/javascripts directory can be referenced here using a relative path.
//
// It's not advisable to add code directly here, but if you do, it'll appear at the bottom of the
// compiled file. JavaScript code in this file should be added after the last require_* statement.
//
// Read Sprockets README (https://github.com/rails/sprockets#sprockets-directives) for details
// about supported directives.
//
//= require jquery
//= require jquery_ujs
//= require turbolinks
//= require_tree .

下面是服务器日志的样子：

Started GET "/" for ::1 at 2016-09-02 09:08:19 -0500
  ActiveRecord::SchemaMigration Load (1.5ms)  SELECT "schema_migrations".* FROM "schema_migrations"
  User Load (1.7ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 ORDER BY "users"."id" ASC LIMIT $2  [["id", 2], ["LIMIT", 1]]
Processing by ProfilesController#index as HTML
  Rendering profiles/index.html.erb within layouts/application
  Profile Load (1.6ms)  SELECT "profiles".* FROM "profiles"
  Rendered profiles/index.html.erb within layouts/application (45.8ms)
Completed 500 Internal Server Error in 367ms (ActiveRecord: 6.3ms)

DEPRECATION WARNING: #original_exception is deprecated. Use #cause instead. (called from initialize at /.rvm/gems/ruby-2.3.1@myapp/gems/better_errors-2.1.1/lib/better_errors/raised_exception.rb:7)
DEPRECATION WARNING: #original_exception is deprecated. Use #cause instead. (called from initialize at /.rvm/gems/ruby-2.3.1myapp/gems/better_errors-2.1.1/lib/better_errors/raised_exception.rb:8)

Sprockets::ArgumentError - require_tree argument must be a directory:
  sprockets (3.7.0) lib/sprockets/directive_processor.rb:182:in `rescue in block in process_directives'
  sprockets (3.7.0) lib/sprockets/directive_processor.rb:179:in `block in process_directives'
  sprockets (3.7.0) lib/sprockets/directive_processor.rb:178:in `process_directives'

我没有使用任何插件。这是一个相当简单/vanilla的应用程序。唯一的样式来自默认的scaffold.scss。
是什么引起的？