Lucene cannot process a conversation and crashes

[AitorAlgorta]

Describe the bug

Some conversations in the DocumentMapper class are being passed as null, which is causing unexpected behavior in the application when trying to index them in Lucene.

To Reproduce

Steps to reproduce the behavior:

1. Installed Airy using the standard installation instructions.
2. Created conversations through the app, then tried to run Kafka Streams to restore state.
3. Observed that some conversations are null, leading to errors during the restore process and indexing.

Expected behavior

Conversations should not be passed as null. Proper validation should be implemented to handle cases where conversations are missing or incomplete without breaking the state restoration process.

Screenshots

N/A

Additional context

• The issue is affecting the fromConversationIndex method in DocumentMapper.java, where some conversations lack required fields such as id, channelId, and createdAt.
• Logs show NullPointerExceptions when attempting to index conversations with missing data.