How to solve the "The following module is missing from the file system" error? I am getting the following error in a Drupal 8 site.


  The following module is missing from the file system


It looks as if a custom module was installed and deleted without uninstalling it. 

How can I fix this error?
If you have Drupal Console then a quick way to fix this is to generate a module with the same machine name, then uninstall it.

$ drupal generate:module


Then type the machine name at the appropriate prompt and accepts defaults for everything else.

$ drush pm-uninstall


Then you can delete the newly generated module from the file system and continue with your day.

(NB you may find need to keep that generated module, else the error will return. In that case, if you need to install a contrib module with the same name, remove the generated module after adding the contrib module. Then clear the cache.)