Ensure guild_ids is never None.

Author: benwoo1110

discord_slash/client.py

@@ -535,7 +535,8 @@ def add_slash_command(
         """
         name = name or cmd.__name__
         name = name.lower()
-        if guild_ids and not all(isinstance(item, int) for item in guild_ids):
+        guild_ids = guild_ids if guild_ids else []
+        if not all(isinstance(item, int) for item in guild_ids):
             raise error.IncorrectGuildIDType(
                 f"The snowflake IDs {guild_ids} given are not a list of integers. Because of discord.py convention, please use integer IDs instead. Furthermore, the command '{name}' will be deactivated and broken until fixed."
             )
@@ -616,7 +617,8 @@ def add_subcommand(
         name = name or cmd.__name__
         name = name.lower()
         description = description or getdoc(cmd)
-        if guild_ids and not all(isinstance(item, int) for item in guild_ids):
+        guild_ids = guild_ids if guild_ids else []
+        if not all(isinstance(item, int) for item in guild_ids):
             raise error.IncorrectGuildIDType(
                 f"The snowflake IDs {guild_ids} given are not a list of integers. Because of discord.py convention, please use integer IDs instead. Furthermore, the command '{name}' will be deactivated and broken until fixed."
             )