Validator does not comply with JSON Schema validation standards

[DanNemes]

Given this schema:

{
   "$schema":"http://json-schema.org/draft-07/schema#",
   "type":"object",
   "properties":{
      "test":{
         "type":"object",
         "properties":{
            "nested":{
               "type":"string",
               "nullable":true,
               "format":"date"
            }
         }
      }
   }
}

This input:

{
  "test":{
      "nested":null
  }
}

And this java snippet

final JsonNode jsonNodeSchema = ObjectMapperUtil.readTree(SCHEMA);
final JsonSchemaFactory factory = JsonSchemaFactory.getInstance(SpecVersionDetector.detect(jsonNodeSchema));
final JsonSchema validator = factory.getSchema(jsonNodeSchema, SchemaValidatorsConfig.builder()
    .nullableKeywordEnabled(false)
    .build());

final JsonNode jsonNodeFromString = ObjectMapperUtil.readTree(DATA);
final Set<ValidationMessage> errors = validator.validate(jsonNodeFromString);
if (!errors.isEmpty()) {
    throw new RuntimeException(errors.toString());
}

Expectation:
An error message to always be shown, irrespective of 'nullable': "/test/nested: null found, string expected"
This is because in the json schema specification the 'nullable' keyword does not exist and setting it to either true/false should have no effect on the validation.

Actual result:
setting the 'nullable' flag in the schema to true: no error message
setting the 'nullable' flag in the schema to false: error message shown "/test/nested: null found, string expected"

Using the same json schema and input on the following site would yield the correct error:
https://www.jsonschemavalidator.net/