I have train my dataset and I have assgined them intent but some of the sentences do not have any entity ? does it effect effect the performance ? should each of the sentence must have the entity and intent to train ?
You don’t necessarily need entities on the training examples.
If your intention is to handle fall back or garbage scenarios, there is a good explanation about them at the below link:
https://blog.spg.ai/failing-gracefully-with-rasa-nlu-14a7d8e53af9
Be wary that modules have been updated since the time of writing the article, and hence refer to latest documentation for the code snippets.
Hope this helps 