Fix default return value for fallback to parent profile.

Author: dkocher

hub/src/main/java/cloud/katta/protocols/hub/serializer/ProxyDeserializer.java

@@ -81,7 +81,7 @@ public Map<String, String> mapForKey(final String key) {
             @Override
             public Boolean booleanForKey(final String key) {
                 log.warn("Unknown key {}", key);
-                return false;
+                return null;
             }
 
             @Override