Change User.avatar to be Optional[Asset] instead of Asset

This change was needed to allow users to more easily check if an
uploaded avatar was set using `if user.avatar:` rather than the
admittedly clunky `if user.avatar != user.default_avatar.

The old behaviour with a fallback is still useful for actual display
purposes, so it has been moved over to the new `User.display_avatar`
attribute. This also has symmetry with the newly added
`Member.display_avatar` attribute.

discord/member.py

@@ -275,7 +275,7 @@ class Member(discord.abc.Messageable, _UserTag):
         system: bool
         created_at: datetime.datetime
         default_avatar: Asset
-        avatar: Asset
+        avatar: Optional[Asset]
         dm_channel: Optional[DMChannel]
         create_dm = User.create_dm
         mutual_guilds: List[Guild]
@@ -513,7 +513,7 @@ class Member(discord.abc.Messageable, _UserTag):
 
         .. versionadded:: 2.0
         """
-        return self.guild_avatar or self.avatar
+        return self.guild_avatar or self._user.avatar or self._user.default_avatar
 
     @property
     def guild_avatar(self) -> Optional[Asset]:

discord/user.py

@@ -147,22 +147,31 @@ class BaseUser(_UserTag):
         return PublicUserFlags._from_value(self._public_flags)
 
     @property
-    def avatar(self) -> Asset:
-        """:class:`Asset`: Returns an :class:`Asset` for the avatar the user has.
+    def avatar(self) -> Optional[Asset]:
+        """Optional[:class:`Asset`]: Returns an :class:`Asset` for the avatar the user has.
 
-        If the user does not have a traditional avatar, an asset for
-        the default avatar is returned instead.
+        If the user does not have a traditional avatar, ``None`` is returned.
+        If you want the avatar that a user has displayed, consider :attr:`display_avatar`.
         """
-        if self._avatar is None:
-            return Asset._from_default_avatar(self._state, int(self.discriminator) % len(DefaultAvatar))
-        else:
+        if self._avatar is not None:
             return Asset._from_avatar(self._state, self.id, self._avatar)
+        return None
 
     @property
     def default_avatar(self) -> Asset:
         """:class:`Asset`: Returns the default avatar for a given user. This is calculated by the user's discriminator."""
         return Asset._from_default_avatar(self._state, int(self.discriminator) % len(DefaultAvatar))
 
+    @property
+    def display_avatar(self) -> Asset:
+        """:class:`Asset`: Returns the user's display avatar.
+
+        For regular users this is just their default avatar or uploaded avatar.
+
+        .. versionadded:: 2.0
+        """
+        return self.avatar or self.default_avatar
+
     @property
     def banner(self) -> Optional[Asset]:
         """Optional[:class:`Asset`]: Returns the user's banner asset, if available.
@@ -248,18 +257,6 @@ class BaseUser(_UserTag):
         """
         return self.name
 
-    @property
-    def display_avatar(self) -> Asset:
-        """:class:`Asset`: Returns the user's display avatar.
-
-        For regular users this is just their avatar, but
-        if they have a guild specific avatar then that
-        is returned instead.
-
-        .. versionadded:: 2.0
-        """
-        return self.avatar
-
     def mentioned_in(self, message: Message) -> bool:
         """Checks if the user is mentioned in the specified message.