'Generation resulted in no candidates matching provided output schema' when optional fields returns null

[RichardH9L]

When the startTime or endTime fields are not extracted from the incomingEmail, it will return null as expected, but it will throw FAILED_PRECONDITION: Generation resulted in no candidates matching provided output schema.

For testing purpose, to see if it's indeed the optional fields causing the issue, I changed startTime?: string to startTime?: null and that made it work.

My understanding is, when using dotprompt, startTime?: string should accept null values.

Using dotprompt

---
model: vertexai/gemini-1.5-pro
config:
  temperature: 0.1
input:
  schema:
    incomingEmail: string
output:
  format: json
  schema:
    intent(enum, intent of email): [availability_check, reservation_change, other]
    date?: string, the date of the desired reservation
    startTime?: string, the start time of the desired reservation
    endTime?: string, the end time of the desired reservation
---

When using zod, z.nullable(z.string()).optional() works, and z.string().optional() does not.

[mbleigh]

This was super annoying to me as well! I recently fixed it in #407 and in the next release nulls should be acceptable.