type string|null with format fails validation for cli utility but not in python directly

[katylava]

Given the following schema:

{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
        "some_date": {
            "type": ["string", "null"],
            "format": "date-time"
        }
    },
    "required": ["some_date"],
    "additionalProperties": false
}

And the following json:

{
  "some_date": null
}

I would expect validation to pass. However it tells me "None is not a 'date-time'":

 ❧ check-jsonschema --schemafile nullable.schema.json nullable-null.json
Schema validation errors were encountered.
  nullable-null.json::$.some_date: None is not a 'date-time'

I would expect it to pass validation since it does when run through the underlying python library:

from jsonschema import validate
from jsonschema import Draft202012Validator

schema = {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
        "some_date": {
            "type": ["string", "null"],
            "format": "date",
        },
    },
    "required": ["some_date"],
}

objs = [
    {"some_date": None},
    {"some_date": "adiofns"}, # included to show that it will error on a string with the incorrect format
    {"some_date": "2023-10-01"},
]

for obj in objs:
    try:
        validate(obj, schema, format_checker=Draft202012Validator.FORMAT_CHECKER)
    except Exception as e:
        print(f"---\nValidation failed for {obj}: {e}")
    else:
        print(f"---\nValidation succeeded for {obj}")

 ❧ python nullable.py
---
Validation succeeded for {'some_date': None}
---
Validation failed for {'some_date': 'adiofns'}: 'adiofns' is not a 'date'

Failed validating 'format' in schema['properties']['some_date']:
    {'type': ['string', 'null'], 'format': 'date'}

On instance['some_date']:
    'adiofns'
---
Validation succeeded for {'some_date': '2023-10-01'}

[sirosen]

Thanks for the super-clear report! I'm guessing that there's a mistake in the customized format checker used in check-jsonschema, but I'll need to run this down to confirm it.