Add comments and update tests

Author: qdpham13

firebase-config/src/main/java/com/google/firebase/remoteconfig/internal/ConfigFetchHandler.java

@@ -575,6 +575,8 @@ public static FetchResponse forBackendUpdatesFetched(
           lastFetchETag);
     }
 
+    // Passing in param fetchedConfigs because it contains templateVersion but no other active
+    // fields.
     public static FetchResponse forBackendHasNoUpdates(
         Date fetchTime, ConfigContainer fetchedConfigs) {
       return new FetchResponse(

firebase-config/src/test/java/com/google/firebase/remoteconfig/internal/ConfigFetchHttpClientTest.java

@@ -161,13 +161,15 @@ public void fetch_newValues_responseSet() throws Exception {
   }
 
   @Test
-  public void fetch_noChange_responseNotSet() throws Exception {
+  public void fetch_noChange_responseOnlyContainsTemplateVersion() throws Exception {
     setServerResponseTo(noChangeResponseBody, SECOND_ETAG);
 
     FetchResponse response = fetch(SECOND_ETAG);
 
     assertThat(response.getLastFetchETag()).isNull();
     assertThat(response.getFetchedConfigs()).isNotNull();
+    assertThat(response.getFetchedConfigs().getTemplateVersionNumber()).isNotNull();
+    assertThat(response.getFetchedConfigs().getConfigs().length()).isEqualTo(0);
   }
 
   @Test