title: magento 2 Required parameter 'theme_dir' was not passed
body: <p>After Theme installation and applied the theme in backend (<strong>System-> Configuration-> General-> Theme</strong>),clear the cache and refresh front end it gives an error in magento2.the error like below</p>
  
  <pre><code>Required parameter 'theme_dir' was not passed
  #0 /var/www/demos/magento2new/vendor/magento/framework/View/Design/Fallback/Rule/Theme.php(69): Magento\Framework\View\Design\Fallback\Rule\Simple-&gt;getPatternDirs(Array)
  #1 /var/www/demos/magento2new/vendor/magento/framework/View/Design/FileResolution/Fallback/Resolver/Simple.php(93): Magento\Framework\View\Design\Fallback\Rule\Theme-&gt;getPatternDirs(Array)
  #2 /var/www/demos/magento2new/vendor/magento/framework/View/Design/FileResolution/Fallback/Resolver/Simple.php(64): Magento\Framework\View\Design\FileResolution\Fallback\Resolver\Simple-&gt;resolveFile(Object(Magento\Framework\View\Design\Fallback\Rule\Theme), 'i18n/en_US.csv', Array)
  #3 /var/www/demos/magento2new/vendor/magento/framework/View/Design/FileResolution/Fallback/LocaleFile.php(42): Magento\Framework\View\Design\FileResolution\Fallback\Resolver\Simple-&gt;resolve('locale', 'i18n/en_US.csv', 'frontend', Object(Magento\Theme\Model\Theme), 'en_US', NULL)
  #4 /var/www/demos/magento2new/vendor/magento/framework/View/FileSystem.php(103): Magento\Framework\View\Design\FileResolution\Fallback\LocaleFile-&gt;getFile('frontend', Object(Magento\Theme\Model\Theme), 'en_US', 'i18n/en_US.csv')
  </code></pre>
  
  <p>added the <code>registration.php</code> in theme but front end is blankpage...</p>