Forward port a missing null instance property test.

Author: Julian

tests/draft-next/unevaluatedProperties.json

@@ -1392,5 +1392,20 @@
                 "valid": true
             }
         ]
+    },
+    {
+        "description": "unevaluatedProperties with null valued instance properties",
+        "schema": {
+            "unevaluatedProperties": {
+                "type": "null"
+            }
+        },
+        "tests": [
+            {
+                "description": "allows null valued properties",
+                "data": {"foo": null},
+                "valid": true
+            }
+        ]
     }
 ]