Cannot Update Empty oneToMany Relationships

Appwrite's updateDocument() API cannot update an empty oneToMany relationship array. When attempting to update an empty relationship with a single-item array, the API returns a relationship_value_invalid error with contradictory error messages.

Environment

• Appwrite Version: Cloud (cloud.appwrite.io)
• SDK: dart_appwrite version ^20.1.0
• Dart SDK: >=3.0.0 <4.0.0
• Relationship Type: oneToMany

Expected Behavior

When a oneToMany relationship array is empty [], we should be able to update it with a single-item array [documentId] to add the first relationship.

Actual Behavior

When attempting to update an empty oneToMany relationship with a single-item array, Appwrite rejects the update with:

AppwriteException: relationship_value_invalid, Invalid relationship value. 
Must be either a document, document ID or null. Array given. (400)

However, the error message is contradictory because:

• When passing an array: "Must be either a document, document ID or null. Array given."
• When passing a single document ID: "Must be either an array of documents or document IDs, string given."
• When passing a document object: "Must be either an array of documents or document IDs, object given."
• When passing null: "Must be either an array of documents or document IDs, NULL given."

This creates a catch-22 situation where no format is accepted when the relationship is empty.

Steps to Reproduce

1. Create a document (parent) with an empty oneToMany relationship array []
2. Create a related document (child)
3. Attempt to update the parent's oneToMany relationship with the child document ID:

We implemented a workaround that:

1. Creates a temporary placeholder document in the related collection
2. Updates the relationship with [placeholderId, childDocumentId] (2 items - this works!)
3. Deletes the placeholder document
4. Updates the relationship again with [childDocumentId] (now works because array is no longer empty)