Empty $type warning at startup

Steps to reproduce

1. Start Magnolia 6
2. Check the startup-logs
3. See the following warning: 

   WARN  a.config.resolver.AnnotationProcessingTypeResolver: Encountered the '$type' property but failed to resolved the type from its value: [{}]. Available types: [jcrStatusColumn,variantAwareNameColumn,enumColumn,iconColumn,referredColumn,unhtmlColumn,columnComponent,jcrTypeColumn,iconAndValueColumn,koosCountColumn,jcrTitleColumn,jcrPathColumn,dateOnlyColumn,dateColumn] 
   
   

Also check line 271 of info/magnolia/map2bean/Map2BeanTransformer.java and line 139 of info/magnolia/config/resolver/AnnotationProcessingTypeResolver.java

The reason why it fails, is that in info/magnolia/personalization/magnolia-personalization-pages/2.0.15/magnolia-personalization-pages-2.0.15.jar!/personalization-pages/decorations/pages-app/apps/pages-app.yaml we have the following piece of configuration:

(...)
workbench:
  contentViews:
    tree:
      columns:
        jcrName:
          $type: !override
          class: info.magnolia.pages.app.browser.column.CachingVariantAwareTitleColumnDefinition
(...) 

Apparently, this is not the way to replace $type with another class; it reports an empty type.

Expected results

No warning should be logged on startup

Actual results

The logs are spammed with 50+ warnings

Workaround

-

Development notes

 the $type: !override can be safely removed and it works