deepEquals() crashes with "type 'Null' is not a subtype of type 'Object'" when comparing maps with different keys

[siddharthadevops]

Labels

• bug
• protobuf
• null-safety

---

Description

The deepEquals() function in protobuf 5.0.0 crashes when comparing GeneratedMessage objects that contain map fields with different keys, throwing the error:

type 'Null' is not a subtype of type 'Object'

This is a regression from protobuf 4.x where such comparisons worked correctly.

Environment

• Package: protobuf
• Version: 5.0.0
• Dart SDK: >=3.5.0 <4.0.0
• Platform: All platforms

Steps to Reproduce

1. Create a protobuf message with a map<K, V> field
2. Create two instances with maps that have the same size but different keys
3. Compare the messages using == operator

Minimal Example

import 'package:protobuf/protobuf.dart';

// Using a protobuf message with: map<uint32, bool> properties = 1;

void main() {
  final msg1 = TestMessage()
    ..properties[1] = true
    ..properties[2] = false;

  final msg2 = TestMessage()
    ..properties[1] = true
    ..properties[3] = true;  // Different key: 3 instead of 2

  // This crashes:
  print(msg1 == msg2);
}

Expected Behavior

The comparison should return false (maps are different) without crashing.

Actual Behavior

The code crashes with:

type 'Null' is not a subtype of type 'Object'
#0      areMapsEqual.<anonymous closure> (package:protobuf/src/protobuf/utils.dart:27:58)
#1      Iterable.every (dart:core/iterable.dart:446:16)
#2      areMapsEqual (package:protobuf/src/protobuf/utils.dart:27:19)
#3      deepEquals (package:protobuf/src/protobuf/utils.dart:13:44)
#4      FieldSet._equalFieldValues (package:protobuf/src/protobuf/field_set.dart:559:47)
#5      FieldSet._equals (package:protobuf/src/protobuf/field_set.dart:517:12)
#6      GeneratedMessage.== (package:protobuf/src/protobuf/generated_message.dart:133:51)

Root Cause

In protobuf 5.0.0, the deepEquals() signature changed from dynamic to non-nullable:

// protobuf 4.x
bool _deepEquals(lhs, rhs) { ... }

// protobuf 5.0.0
bool deepEquals(Object lhs, Object rhs) { ... }  // Non-nullable!

However, areMapsEqual() can pass null when accessing a key that doesn't exist:

bool areMapsEqual(Map lhs, Map rhs) {
  if (lhs.length != rhs.length) return false;
  return lhs.keys.every((key) => deepEquals(lhs[key], rhs[key]));
  //                                        ^^^^^^^^  ^^^^^^^^
  //                                        Can be null!
}

Proposed Solution

Make deepEquals accept nullable parameters:

bool deepEquals(Object? lhs, Object? rhs) {
  // Handle null cases first
  if (lhs == null || rhs == null) return lhs == rhs;
  // ... rest of the function unchanged
}

Files to Modify

• protobuf/lib/src/protobuf/utils.dart (line 8)

Impact

This affects:

• Any code comparing protobuf messages with map<K, V> fields
• Production applications using protobuf 5.0.0
• Migration from protobuf 4.x to 5.x

[osa1]

Thanks for reporting. Fix published with protobuf 5.1.0.