fix(remote_config)!: check value types before passing them to native (#6817)

* fix(remote_config)!: check value types before passing them to native

BREAKING CHANGE: #setDefaults now throws if non-primitive value is being passed.
We're being explicit about value types to prevent serialization of complex objects on native side, making them non-deserializable

* fix(remote_config): apply correct condition

* refactor(remote_config): concat exception message lines

* refactor(remote_config): move params check logic out of the meethod channel

* test(remote_config): verify #setDefaults checks for argument type

* doc(remote_config): being explicit about value types

* refactor(remote_config): throw ArgumentError with more verbose description

Author: lesnitsky

packages/firebase_remote_config/firebase_remote_config/lib/src/remote_config.dart

@@ -132,7 +132,19 @@ class RemoteConfig extends FirebasePluginPlatform with ChangeNotifier {
   }
 
   /// Sets the default parameter values for the current instance.
+  /// Only booleans, strings and numbers are supported as values of the map
   Future<void> setDefaults(Map<String, dynamic> defaultParameters) {
+    defaultParameters.forEach(_checkIsSupportedType);
     return _delegate.setDefaults(defaultParameters);
   }
+
+  void _checkIsSupportedType(String key, dynamic value) {
+    if (value is! bool && value is! num && value is! String) {
+      throw ArgumentError(
+        'Invalid value type "${value.runtimeType}" for key "$key". '
+        'Only booleans, numbers and strings are supported as config values. '
+        "If you're trying to pass a json object – convert it to string beforehand",
+      );
+    }
+  }
 }

packages/firebase_remote_config/firebase_remote_config/test/firebase_remote_config_test.dart

@@ -213,6 +213,15 @@ void main() {
         remoteConfig.setDefaults(mockParameters);
         verify(mockRemoteConfigPlatform.setDefaults(mockDefaultParameters));
       });
+
+      test('should throw when non-primitive value is passed', () {
+        expect(
+          () => remoteConfig.setDefaults({
+            'key': {'nested': 'object'}
+          }),
+          throwsArgumentError,
+        );
+      });
     });
   });
 }