jsonschema issue

issue.py

import json
from jsonschema import ValidationError, validate
from jsonschema import Draft4Validator, Draft6Validator, Draft7Validator

schema = {
    "type" : "object",
    "required": ["name"],
    "properties" : {
        "name" : {
            "type" : "string"
        },
        "nr_periods" : {
            "type": "integer",
            "maximum": 2147483647,
            "minimum": -2147483648
        },
        "initial_date" : {
            "type": "string",
            "format": "date",
            "nullable": True,
            #"default": None,
        },
    },
}

schema_wrapper = {
    # "openapi": "3.0.0",
    "schemas": schema
}



def test_validate(data, schema, **kwargs):
    print()
    try:
        json_data = json.loads(data)
        validate(json_data, schema, **kwargs)
        print("Valid. Data: %s" % data)
    except ValidationError as e:
        print("Invalid. Data %s. Exc: %s" % (data, str(e)))


data = """
{
"name": "a name",
"nr_periods": 1
}
"""
test_validate(data, schema) # OK
test_validate(data, schema_wrapper) # OK

data = """
{
"name": "a name",
"nr_periods": 1,
"initial_date": null
}
"""

test_validate(data, schema) # Expected valid but it's invalid
test_validate(data, schema_wrapper) # OK

output.txt

Valid. Data: 
{
"name": "a name",
"nr_periods": 1
}


Valid. Data: 
{
"name": "a name",
"nr_periods": 1
}


Invalid. Data 
{
"name": "a name",
"nr_periods": 1,
"initial_date": null
}
. Exc: None is not of type 'string'

Failed validating 'type' in schema['properties']['initial_date']:
    {'format': 'date', 'nullable': True, 'type': 'string'}

On instance['initial_date']:
    None

Valid. Data: 
{
"name": "a name",
"nr_periods": 1,
"initial_date": null
}