Fix reference errors when importing an exported ZIP Tree XML Export

In studio

• Create a document type called Author
• Create a document type called Book, add an attribute called "author" to the schema that is of type "Document" (to reference the Author)
• In Book creation layout add the field "author" and be sure that the NXQL query you select an author

In platform

• Create a Workspace
• Create a folder "Library"
• Create a folder "A" (we will put a book here)
• Create a folder "Z" ( we will put an author here)
• In folder Z create an author A1
• In folder A create a book B1 that references author A1
• Go to folder "Library"
• Click on "ZIP Tree XML Export"
• Remove folder "Library"
• Go the the trash and remove the folder "Library" permanently
• Import the exported zip using the web import

You'll have the issue saying org.nuxeo.ecm.core.api.validation.DocumentValidationException: Constraint violation thrown: '"05e9d36d-ddb0-4..." is not a valid document id.'

Because it was trying to resolve the dependency to the id that doesn't exist anymore.

This case blocks from exporting a zip structure (with references) in a platform and importing it in another.