DOCSP-45803: atlas search queries null & guid values (#582)

(cherry picked from commit 041dced)

Author: rustagir

source/fundamentals/atlas-search.txt

@@ -73,6 +73,8 @@ categorizes data in a searchable format.
 To learn how to create an Atlas Search Index see the
 :atlas:`Create an Atlas Search Index </atlas-search/create-index>` Atlas guide.
 
+.. _csharp-atlas-search-operators:
+
 Atlas Search Operators and Collectors
 -------------------------------------
 

source/whats-new.txt

@@ -87,6 +87,16 @@ The 3.1 driver release includes the following new features:
   builders for the ``equals`` operator. To learn more about using Atlas Search with the
   {+driver-short+}, see :ref:`csharp-atlas-search`.
 
+- Adds support for the following Atlas Search queries:
+
+  - Using the ``Equals()`` operator method on ``null`` and ``Guid`` values
+
+  - Using the ``In()`` operator method on ``Guid`` values
+
+  To learn more about these methods, see the
+  :ref:`csharp-atlas-search-operators` section of the Atlas Search
+  guide.
+
 - Adds support for sequential pagination in Atlas Search.
 
 - Adds support for valid SRV hostnames with fewer than 3 parts.