Fix json data type for empty string

tests/test_internal_controller.py

@@ -100,7 +100,7 @@ class TestInternalController(BaseTestCase):
         Log health info
         """
         body = {
-            "details": {},
+            "details": "",
             "isHealthy": True,
             "logTime": "2014-11-21T17:16:23+01:00",
         }