How do  you do zero parameters with zod

### Please read this first

The below doesn't work, but nothing else seems to work either.

### Question

Describe your question. Provide details if available.
```typescript
const getSFWeatherTool = tool({
  name: 'get_weather',
  description: 'Get the weather for SF',
  parameters: z.object({}),
  execute: async () => {
    return `The weather in SF is sunny`;
  },
});
```