Fix nullable issue (#1134)

Author: justin-tay

src/main/java/com/networknt/schema/utils/JsonNodeUtil.java

@@ -84,10 +84,9 @@ public static boolean equalsToSchemaType(JsonNode node, JsonType schemaType, Jso
             }
 
             if (nodeType == JsonType.NULL) {
-                if (parentSchema != null) {
+                if (parentSchema != null && config.isNullableKeywordEnabled()) {
                     JsonSchema grandParentSchema = parentSchema.getParentSchema();
-                    if (grandParentSchema != null
-                            && JsonNodeUtil.isNodeNullable(grandParentSchema.getSchemaNode(), config)
+                    if (grandParentSchema != null && JsonNodeUtil.isNodeNullable(grandParentSchema.getSchemaNode())
                             || JsonNodeUtil.isNodeNullable(parentSchema.getSchemaNode())) {
                         return true;
                     }

src/test/java/com/networknt/schema/TypeValidatorTest.java

@@ -149,4 +149,36 @@ void walkNull() {
         ValidationResult result = schema.walk(null, true);
         assertTrue(result.getValidationMessages().isEmpty());
     }
+
+    @Test
+    void nullable() {
+        String schemaData = "{\r\n"
+                + "   \"$schema\":\"http://json-schema.org/draft-07/schema#\",\r\n"
+                + "   \"type\":\"object\",\r\n"
+                + "   \"properties\":{\r\n"
+                + "      \"test\":{\r\n"
+                + "         \"type\":\"object\",\r\n"
+                + "         \"properties\":{\r\n"
+                + "            \"nested\":{\r\n"
+                + "               \"type\":\"string\",\r\n"
+                + "               \"nullable\":true,\r\n"
+                + "               \"format\":\"date\"\r\n"
+                + "            }\r\n"
+                + "         }\r\n"
+                + "      }\r\n"
+                + "   }\r\n"
+                + "}";
+        String inputData = "{\r\n"
+                + "  \"test\":{\r\n"
+                + "      \"nested\":null\r\n"
+                + "  }\r\n"
+                + "}";
+        final JsonSchemaFactory factory = JsonSchemaFactory.getInstance(VersionFlag.V7);
+        final JsonSchema validator = factory.getSchema(schemaData, SchemaValidatorsConfig.builder()
+            .nullableKeywordEnabled(false)
+            .build());
+
+        final Set<ValidationMessage> errors = validator.validate(inputData, InputFormat.JSON);
+        assertEquals(1, errors.size());
+    }
 }