Return null when calling toString on a null object (#1693)

pkgs/jni/CHANGELOG.md

@@ -4,6 +4,7 @@
   through method channels. You can send the address of the pointer as `long` and
   reconstruct the class using the helper method.
 - Fixed a bug where it would be possible for a type class inference to fail.
+- Return 'null' when calling `toString` on a null object.
 
 ## 0.12.0
 

pkgs/jni/lib/src/jobject.dart

@@ -127,6 +127,9 @@ class JObject {
       _class.instanceMethodId(r'toString', r'()Ljava/lang/String;');
   @override
   String toString() {
+    if (reference.isNull) {
+      return 'null';
+    }
     return _toStringId(this, const JStringType(), [])
         .toDartString(releaseOriginal: true);
   }

pkgs/jni/test/jobject_test.dart

@@ -296,4 +296,16 @@ void run({required TestRunnerCallback testRunner}) {
       throwsA(isA<AssertionError>()),
     );
   });
+
+  testRunner('toString', () {
+    final long = JLong(1);
+    expect(
+      long.toString(),
+      '1',
+    );
+    expect(
+      JLong.fromReference(jNullReference).toString(),
+      'null',
+    );
+  });
 }