I've tried unsetting it via select and it doesn't clear it out. I've tried setting assistantId: null | undefined via API and it doesn't clear it. How do you remove an assistant for a phone number? We are trying to use retrieving assistants: https://docs.vapi.ai/server-url/events#retrieving-assistants https://cdn.discordapp.com/attachments/1382194151847759912/1382194152141230280/CleanShot_2025-06-10_at_22.02.492x.png?ex=684a441d&is=6848f29d&hm=cf68a21ad45441d449a3a79215b3e62ed0b3cb7507b105320137b43f71ec17ff&