nullish vs optional vs nullable in Zod

.optional()

• Type: T | undefined
• Accepts: undefined, missing key in objects, any value passing the base schema T
• Rejects: null (unless separately allowed)
• Shorthand for "allow the value to be absent"

.nullable()

• Type: T | null
• Accepts: explicit null, any value passing T
• Rejects: undefined, missing key
• Purpose: value must be supplied but may be null

.nullish()

• Type: T | null | undefined
• Accepts: null, , missing key, any value passing