sqliteからmysqlへ変更し、その後rails :db:createコマンドを実行しデータベースの作成を試みたところ次のようなエラーが出てしまいました。

rails db:create
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/2.5.0/fileutils.rb:90: warning: already initialized constant FileUtils::VERSION
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/fileutils-1.4.1/lib/fileutils.rb:105: warning: previous definition of VERSION was here
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/2.5.0/fileutils.rb:1188: warning: already initialized constant FileUtils::Entry_::S_IF_DOOR
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/fileutils-1.4.1/lib/fileutils.rb:1284: warning: previous definition of S_IF_DOOR was here
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/2.5.0/fileutils.rb:1446: warning: already initialized constant FileUtils::Entry_::DIRECTORY_TERM
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/fileutils-1.4.1/lib/fileutils.rb:1568: warning: previous definition of DIRECTORY_TERM was here
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/2.5.0/fileutils.rb:1501: warning: already initialized constant FileUtils::OPT_TABLE
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/fileutils-1.4.1/lib/fileutils.rb:1626: warning: previous definition of OPT_TABLE was here
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/2.5.0/fileutils.rb:1555: warning: already initialized constant FileUtils::LOW_METHODS
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/fileutils-1.4.1/lib/fileutils.rb:1685: warning: previous definition of LOW_METHODS was here
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/2.5.0/fileutils.rb:1562: warning: already initialized constant FileUtils::METHODS
/Users/apple/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/fileutils-1.4.1/lib/fileutils.rb:1692: warning: previous definition of METHODS was here
rails aborted!
ActiveRecord::DatabaseConfigurations::InvalidConfigurationError: '{ default =>  }' is not a valid configuration. Expected '' to be a URL string or a Hash.
/Users/apple/create/portfolio/Rakefile:6:in `<top (required)>'
/Users/apple/create/portfolio/bin/rails:9:in `<top (required)>'
/Users/apple/create/portfolio/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'

Caused by:
Bootsnap::LoadPathCache::FallbackScan: 

(See full trace by running task with --trace)

また、sqliteからmysqlへ変更した際にdatabase.ymlも変更したのでそちらも載せておきます。

 default: &default
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: root
  password: password  #<- mysqlインストール時に設定したパスワード  例: 1
  socket: /var/lib/mysql/mysql.sock

development:
  <<: *default
  database: アプリ名_development     #アプリ名_development

test:
  <<: *default
  database: アプリ名_test     #アプリ名_test

production:
  <<: *default
  database:  アプリ名_production     #アプリ名_production
  username: アプリ名     #アプリ名
  password: <%= ENV['TESTMYSQL_DATABASE_PASSWORD'] %>