When updating existing document and document was deleted before the save, a partial document is created

[TamarNevo]

To reproduce, use the following steps:

1. user 1 reads document 1 (or - read document 1 into variable v1)
2. user 2 reads document 1 (or - read document 1 into variable v2)
3. user 1 deletes document 1 (or - perform v1.delete())
4. user 2 updates one field in document 1 (or - change value of one field in v2, and perform v2.save())
   The result is - document 1 is re-created with only one field.

The expected behavior in this case is failure of the update operation. This can be achieved by using upsert=False.

In document.py, _save_update() is using upsert=True when no save_condition is requested.
There is no actual need to use upsert=True since this method is called for updating an existing document (New documents are handled in _save_insert).

[wojcikstefan]

Thank you for reporting it @TamarNevo! That said, there already exists an issue for this problem: #564 (consider leaving a thumbs-up on it).