Throw structured exception from getEnrolledBiometrics

packages/local_auth/local_auth_android/android/src/main/java/io/flutter/plugins/localauth/LocalAuthPlugin.java

@@ -65,6 +65,9 @@ public LocalAuthPlugin() {}
 
   @Override
   public @NonNull List<AuthClassification> getEnrolledBiometrics() {
+    if (biometricManager == null) {
+      return null;
+    }
     ArrayList<AuthClassification> biometrics = new ArrayList<>();
     if (biometricManager.canAuthenticate(BiometricManager.Authenticators.BIOMETRIC_WEAK)
         == BiometricManager.BIOMETRIC_SUCCESS) {

packages/local_auth/local_auth_android/android/src/main/java/io/flutter/plugins/localauth/Messages.java

@@ -586,8 +586,11 @@ public interface LocalAuthApi {
     Boolean stopAuthentication();
     /**
      * Returns the biometric types that are enrolled, and can thus be used without additional setup.
+     *
+     * <p>Returns null if there is no activity, in which case the enrolled biometrics can't be
+     * determined.
      */
-    @NonNull
+    @Nullable
     List<AuthClassification> getEnrolledBiometrics();
     /**
      * Attempts to authenticate the user with the provided [options], and using [strings] for any

packages/local_auth/local_auth_android/android/src/test/java/io/flutter/plugins/localauth/LocalAuthTest.java

@@ -274,6 +274,14 @@ public void onDetachedFromActivity_ShouldReleaseActivity() {
     assertNull(plugin.getActivity());
   }
 
+  @Test
+  public void getEnrolledBiometrics_shouldReturnNullForNoActivity() {
+    final LocalAuthPlugin plugin = new LocalAuthPlugin();
+
+    final List<AuthClassification> enrolled = plugin.getEnrolledBiometrics();
+    assertNull(enrolled);
+  }
+
   @Test
   public void getEnrolledBiometrics_shouldReturnEmptyList_withoutHardwarePresent() {
     final LocalAuthPlugin plugin = new LocalAuthPlugin();

packages/local_auth/local_auth_android/lib/local_auth_android.dart

@@ -120,7 +120,13 @@ class LocalAuthAndroid extends LocalAuthPlatform {
 
   @override
   Future<List<BiometricType>> getEnrolledBiometrics() async {
-    final List<AuthClassification> result = await _api.getEnrolledBiometrics();
+    final List<AuthClassification>? result = await _api.getEnrolledBiometrics();
+    if (result == null) {
+      throw const LocalAuthException(
+        code: LocalAuthExceptionCode.uiUnavailable,
+        description: 'No Activity available.',
+      );
+    }
     return result.map((AuthClassification value) {
       switch (value) {
         case AuthClassification.weak:

packages/local_auth/local_auth_android/lib/src/messages.g.dart

@@ -323,7 +323,10 @@ class LocalAuthApi {
 
   /// Returns the biometric types that are enrolled, and can thus be used
   /// without additional setup.
-  Future<List<AuthClassification>> getEnrolledBiometrics() async {
+  ///
+  /// Returns null if there is no activity, in which case the enrolled
+  /// biometrics can't be determined.
+  Future<List<AuthClassification>?> getEnrolledBiometrics() async {
     final String pigeonVar_channelName =
         'dev.flutter.pigeon.local_auth_android.LocalAuthApi.getEnrolledBiometrics$pigeonVar_messageChannelSuffix';
     final BasicMessageChannel<Object?> pigeonVar_channel =
@@ -342,14 +345,9 @@ class LocalAuthApi {
         message: pigeonVar_replyList[1] as String?,
         details: pigeonVar_replyList[2],
       );
-    } else if (pigeonVar_replyList[0] == null) {
-      throw PlatformException(
-        code: 'null-error',
-        message: 'Host platform returned null value for non-null return value.',
-      );
     } else {
-      return (pigeonVar_replyList[0] as List<Object?>?)!
-          .cast<AuthClassification>();
+      return (pigeonVar_replyList[0] as List<Object?>?)
+          ?.cast<AuthClassification>();
     }
   }
 

packages/local_auth/local_auth_android/pigeons/messages.dart

@@ -130,7 +130,10 @@ abstract class LocalAuthApi {
 
   /// Returns the biometric types that are enrolled, and can thus be used
   /// without additional setup.
-  List<AuthClassification> getEnrolledBiometrics();
+  ///
+  /// Returns null if there is no activity, in which case the enrolled
+  /// biometrics can't be determined.
+  List<AuthClassification>? getEnrolledBiometrics();
 
   /// Attempts to authenticate the user with the provided [options], and using
   /// [strings] for any UI.

packages/local_auth/local_auth_android/test/local_auth_test.dart

@@ -85,6 +85,21 @@ void main() {
 
       expect(result, <BiometricType>[]);
     });
+
+    test('throws no UI for null', () async {
+      when(api.getEnrolledBiometrics()).thenAnswer((_) async => null);
+
+      expect(
+        () async => plugin.getEnrolledBiometrics(),
+        throwsA(
+          isA<LocalAuthException>().having(
+            (LocalAuthException e) => e.code,
+            'code',
+            LocalAuthExceptionCode.uiUnavailable,
+          ),
+        ),
+      );
+    });
   });
 
   group('authenticate', () {

packages/local_auth/local_auth_android/test/local_auth_test.mocks.dart

@@ -72,14 +72,12 @@ class MockLocalAuthApi extends _i1.Mock implements _i2.LocalAuthApi {
           as _i4.Future<bool>);
 
   @override
-  _i4.Future<List<_i2.AuthClassification>> getEnrolledBiometrics() =>
+  _i4.Future<List<_i2.AuthClassification>?> getEnrolledBiometrics() =>
       (super.noSuchMethod(
             Invocation.method(#getEnrolledBiometrics, []),
-            returnValue: _i4.Future<List<_i2.AuthClassification>>.value(
-              <_i2.AuthClassification>[],
-            ),
+            returnValue: _i4.Future<List<_i2.AuthClassification>?>.value(),
           )
-          as _i4.Future<List<_i2.AuthClassification>>);
+          as _i4.Future<List<_i2.AuthClassification>?>);
 
   @override
   _i4.Future<_i2.AuthResult> authenticate(