Command error exception is empty

I have a simple error handler for my bot whenever an error occurs. This code used to work when I used 0.0.53 but after updating to 0.0.55, it broke.

@lightbulb.listener(lightbulb.events.CommandErrorEvent)
async def on_command_error(self, event):
    channel = await self.bot.rest.fetch_channel(event.message.channel_id)
    await channel.send(f"An error occured: {event.exception}")
    return

Before update it worked,

But after update, it doesn't work,