Zod not returning undefined

created: z.string().nullish().transform((val) => {
      return val ? new Date(val) : undefined;
    }),

[TypeScript]       Types of property 'creationDate' are incompatible.
[TypeScript]         Type '(Date | ((params?: RawCreateParams) => ZodUndefined)) & (Date | ((params?: RawCreateParams) => ZodUndefined) | undefined)' is not assignable to type 'string | Date | NullableDateTimeFieldUpdateOperationsInput | null | undefined'.
[TypeScript]           Type '(params?: RawCreateParams) => ZodUndefined' is not assignable to type 'string | Date | NullableDateTimeFieldUpdateOperationsInput | null | undefined'.
[TypeScript] 
[TypeScript] 308               update: whois