How to support empty strings for z.string().datetime({ offset: true }).nullish()

How to support empty strings for z.string().datetime({ offset: true }).nullish() schema if the string value is empty, I want it converted to null or keep the original value ie., ""

the following code throw error

import { afterAll, beforeAll } from 'vitest';
import { z } from 'zod';


describe('Test zod validations', () => {

	it('should correctly handles a valid ISO date-string', () => {
		const valid_from = '2022-12-14T22:07:10.430805+00:00';
		const valid_to = undefined; <-- this works
                 const valid_to = null; <-- this works
                 const valid_to =""; <-- this is not working


		const schema = z.string().datetime({ offset: true }).nullish();

		expect(schema.parse(valid_from)).toStrictEqual(valid_from);
		expect(schema.parse(valid_to)).toStrictEqual(valid_to);
	});
});

ERROR

ZodError: [
  {
    "code": "invalid_string",
    "validation": "datetime",
    "message": "Invalid datetime",
    "path": []
  }
]


Serialized Error: {
  "addIssue": "Function<>",
  "addIssues": "Function<>",
  "errors": [
    {
      "code": "invalid_string",
      "message": "Invalid datetime",
      "path": [],
      "validation": "datetime",
    },
  ],
  "flatten": "Function<flatten>",
  "formErrors": {
    "fieldErrors": {},
    "formErrors": [
      "Invalid datetime",
    ],
  },
  "format": "Function<format>",
  "isEmpty": false,
  "issues": [
    {
      "code": "invalid_string",
      "message": "Invalid datetime",
      "path": [],
      "validation": "datetime",
    },
  ],
}

[samchungy]

I think the workarounds are sufficient here. I don’t think any of the other string validators would accept an empty string as a valid option.

You wouldn’t consider an empty string as a valid date

[xmlking]

Wish we have built-in z.nuller like z.coerce

z.nuller.string().datetime({ offset: true }).nullish()

My reusable solution:

export function emptyToNull(arg: unknown) {
	if (typeof arg !== 'string') {
		return arg;
	}
	if (arg.trim() === '') {
		return null;
	}
	return arg;
}


const valid_to = '';
const emptySchema = z.preprocess(emptyToNull, z.string().datetime({ offset: true }).nullish());
expect(emptySchema.parse(valid_to)).toStrictEqual(null);

another workaround:

const emptySchema =  z.string().datetime({ offset: true }).nullish().catch(null);