In different cases we have to display the name/title of a document. Currently not all documents support this.
Add a __toString function to the content document
Add the __toString function to all document types (you can refer to the Solr configuration for the "title" field to see the data it need to contain
You will need to make the Content document abstract, because it can't have a __toString
An implementation has already been created, but was denied:
Each document that extends directly from the Content document needs to implement a __toString() function.