DOCSP-27221 $atan2 NaN/null fix (#2443)

Author: kennethdyer

source/reference/operator/aggregation/atan2.txt

@@ -45,12 +45,10 @@ Behavior
 ``null`` and ``NaN``
 ~~~~~~~~~~~~~~~~~~~~
 
-If the first argument to :expression:`$atan2` is ``null``,
-:expression:`$atan2` returns ``null``. If the first argument to
-:expression:`$atan2` is ``NaN``, :expression:`$atan2` returns ``NaN``.
-If the first argument resolves to a number *and* the 
-second argument resolves to either ``NaN`` or ``null``, 
-:expression:`$atan2` returns the ``NaN`` or ``null`` respectively.
+If either argument given to ``$atan2`` is ``null``, the expression returns
+``null``.  If either argument is ``NaN``, the expression returns ``NaN``.
+If one argument is ``null`` and the other is ``NaN``, the expression returns
+``null``.
 
 
 .. list-table::
@@ -61,21 +59,24 @@ second argument resolves to either ``NaN`` or ``null``,
      - Results
 
    * - ``{ $atan2: [ NaN, <value> ] }``
+     - ``NaN``
 
-       *or*
-
-       ``{ $atan2: [ <value>, NaN ] }``
-     
+   * -  ``{ $atan2: [ <value>, NaN ] }``
      - ``NaN``
 
    * - ``{ $atan2: [ null, <value> ] }``
-     
-       *or*
+     - ``null``
 
-       ``{ $atan2: [ <value>, null ] }``
+   * - ``{ $atan2: [ <value>, null ] }``
+     - ``null``
 
+   * - ``{ $atan2: [ NaN, null ] }``
      - ``null``
 
+   * - ``{ $atan2: [ null, NaN ] }``
+     - ``null``
+
+
 Example
 -------