DOCSP-27226 - Storing null values (#155)

* add admonition

Co-authored-by: Chris Cho <[email protected]>

Author: mongoKart

source/write-to-mongodb.txt

@@ -27,3 +27,8 @@ Write to MongoDB
        content: |
 
          .. include:: /scala/write-to-mongodb.txt
+
+.. important::
+
+   If your write operation includes a field with a ``null`` value,
+   the connector writes the field name and ``null`` value to MongoDB.