🍻 adjust None for UniMessage.generate

Author: RF-Tar-Railt

src/nonebot_plugin_alconna/uniseg/message.py

@@ -1220,7 +1220,7 @@ async def generate(
         bot: Bot | None = None,
         adapter: str | None = None,
     ) -> UniMessage:
-        if not message:
+        if message is None:
             if not event:
                 try:
                     event = current_event.get()
@@ -1255,7 +1255,7 @@ def generate_sync(
         bot: Bot | None = None,
         adapter: str | None = None,
     ) -> UniMessage:
-        if not message:
+        if message is None:
             if not event:
                 try:
                     event = current_event.get()