Update based on review comments

Author: qdpham13

firebase-config/src/main/java/com/google/firebase/remoteconfig/FirebaseRemoteConfigException.java

@@ -21,21 +21,21 @@
 
 /** Base class for {@link FirebaseRemoteConfig} exceptions. */
 public class FirebaseRemoteConfigException extends FirebaseException {
+  /** Code that specifies the type of exception. */
+  private final Code code;
+
   /** Creates a Firebase Remote Config exception with the given message. */
   public FirebaseRemoteConfigException(@NonNull String detailMessage) {
     super(detailMessage);
-    this.code = null;
+    this.code = Code.UNKNOWN;
   }
 
   /** Creates a Firebase Remote Config exception with the given message and cause. */
   public FirebaseRemoteConfigException(@NonNull String detailMessage, @Nullable Throwable cause) {
     super(detailMessage, cause);
-    this.code = null;
+    this.code = Code.UNKNOWN;
   }
 
-  /** Code that specifies the type of exception. */
-  @Nullable private final Code code;
-
   /** Creates a Firebase Remote Config exception with the given message and Code. */
   public FirebaseRemoteConfigException(@NonNull String detailMessage, @NonNull Code code) {
     super(detailMessage);
@@ -89,10 +89,5 @@ private static SparseArray<Code> buildCodeList() {
       }
       return codes;
     }
-
-    @NonNull
-    public static Code fromValue(int value) {
-      return CODE_LIST.get(value, Code.UNKNOWN);
-    }
   }
 }

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

@@ -103,7 +103,7 @@ public void listenForNotifications() {
       } catch (IOException ex) {
         propagateErrors(
             new FirebaseRemoteConfigClientException(
-                "Unable to parse ConfigUpdate.",
+                "Unable to parse config update message.",
                 ex.getCause(),
                 FirebaseRemoteConfigException.Code.CONFIG_UPDATE_MESSAGE_UNAVAILABLE));
       } finally {