[commands] Mention that dynamic_cooldown callable can return None

discord/ext/commands/core.py

@@ -1947,7 +1947,8 @@ def dynamic_cooldown(cooldown, type=BucketType.default):
 
     This differs from :func:`.cooldown` in that it takes a function that
     accepts a single parameter of type :class:`.discord.Message` and must
-    return a :class:`.Cooldown`
+    return a :class:`.Cooldown` or ``None``. If ``None`` is returned then
+    that cooldown is effectively bypassed.
 
     A cooldown allows a command to only be used a specific amount
     of times in a specific time frame. These cooldowns can be based
@@ -1964,9 +1965,9 @@ def dynamic_cooldown(cooldown, type=BucketType.default):
 
     Parameters
     ------------
-    cooldown: Callable[[:class:`.discord.Message`], :class:`.Cooldown`]
+    cooldown: Callable[[:class:`.discord.Message`], Optional[:class:`.Cooldown`]]
         A function that takes a message and returns a cooldown that will
-        apply to this invocation
+        apply to this invocation or ``None`` if the cooldown should be bypassed.
     type: :class:`.BucketType`
         The type of cooldown to have.
     """