DOCSP-24795 updates getKey / getKeyByAltName return types (#1756)

* DOCSP-24795 updates getKey / getKeyByAltName return types

* internal review feedback

* external review clarification

Author: jmd-mongo

source/reference/method/KeyVault.getKey.txt

@@ -35,9 +35,10 @@ KeyVault.getKey()
 
      Document representing a matching data encryption key.
 
-     Returns nothing if no key in the key vault has the specified
-     ``UUID``.
-
+     If no matching data encryption key is found, 
+     ``KeyVault.getKey()`` returns an object containing a hint that no
+     key was found.
+     
 Behavior
 --------
 

source/reference/method/KeyVault.getKeyByAltName.txt

@@ -30,8 +30,9 @@ KeyVault.getKeyByAltName()
 
      Document representing a matching data encryption key.
 
-     Returns nothing if no data encryption key has the specified
-     ``keyAltName``.
+     If no matching data encryption key is found, 
+     ``KeyVault.getKeyByAltName()`` returns an object containing a hint
+     that no key was found.
 
 Behavior
 --------