bpo-38771: Explict test for None in code example (GH-17108)

Author: jonathan-scholbach

Doc/library/collections.rst

@@ -162,7 +162,7 @@ environment variables which in turn take precedence over default values::
         parser.add_argument('-u', '--user')
         parser.add_argument('-c', '--color')
         namespace = parser.parse_args()
-        command_line_args = {k:v for k, v in vars(namespace).items() if v}
+        command_line_args = {k: v for k, v in vars(namespace).items() if v is not None}
 
         combined = ChainMap(command_line_args, os.environ, defaults)
         print(combined['color'])