Define zero argument contructoris for the serializer

Change-Id: I1c5f4a526f886ffb85b1a9d03d661161f66d076b

@@ -39,6 +39,12 @@ public final class ContinuousResource implements Resource {
         this.value = value;
     }
 
+    // for serializer
+    ContinuousResource() {
+        this.id = null;
+        this.value = 0;
+    }
+
     @Override
     public ContinuousResourceId id() {
         return id;

@@ -46,6 +46,12 @@ public final class ContinuousResourceId extends ResourceId {
         this.name = last.getSimpleName();
     }
 
+    // for serializer
+    ContinuousResourceId() {
+        this.components = ImmutableList.of();
+        this.name = "";
+    }
+
     ImmutableList<Object> components() {
         return components;
     }