gh-118820: Zero-valued flag enum has no name (GH-118848)

Co-authored-by: Bénédikt Tran <[email protected]>

Author: nineteendo

Doc/howto/enum.rst

@@ -1152,6 +1152,14 @@ the following are true:
     >>> (Color.RED | Color.GREEN).name
     'RED|GREEN'
 
+    >>> class Perm(IntFlag):
+    ...     R = 4
+    ...     W = 2
+    ...     X = 1
+    ...
+    >>> (Perm.R & Perm.W).name is None  # effectively Perm(0)
+    True
+
 - multi-bit flags, aka aliases, can be returned from operations::
 
     >>> Color.RED | Color.BLUE