TYPO3 Core

Currently an exception is thrown if a YAML file is not found.

In some cases it may be that a YAML file is not available, or only available if a extension installed.

As example if the new Site configuration with the routeEnhancers.
An extension could have its own default route configuration. but if the extension is not installed and the site configuration has a import for this extension, the exception broke the entire TYPO3 installation.

My suggestion would be to optionally make imports optional, like:

imports:
  - 
    resource: "EXT:my_ext/Configuration/Routes/Default.yaml" 
    optional: 1