Fix enum converter not handling null properly

moor/lib/src/runtime/types/custom_type.dart

@@ -22,7 +22,7 @@ abstract class TypeConverter<D, S> {
 
 /// Implementation for an enum to int converter that uses the index of the enum
 /// as the value stored in the database.
-class EnumIndexConverter<T> extends TypeConverter<T, int> {
+class EnumIndexConverter<T> extends NullAwareTypeConverter<T, int> {
   /// All values of the enum.
   final List<T> values;
 
@@ -30,13 +30,15 @@ class EnumIndexConverter<T> extends TypeConverter<T, int> {
   const EnumIndexConverter(this.values);
 
   @override
-  T? mapToDart(int? fromDb) {
+  T requireMapToDart(int fromDb) {
-    return fromDb == null ? null : values[fromDb];
+    return values[fromDb];
   }
 
   @override
-  int? mapToSql(T? value) {
+  int requireMapToSql(T value) {
-    return (value as dynamic)?.index as int;
+    // In Dart 2.14: Cast to Enum instead of dynamic. Also add Enum as an upper
+    // bound for T.
+    return (value as dynamic).index as int;
   }
 }
 

moor/test/types/enum_index_converter_test.dart

@@ -0,0 +1,21 @@
+import 'package:moor/moor.dart';
+import 'package:test/test.dart';
+
+enum _MyEnum { one, two, three }
+
+void main() {
+  const converter = EnumIndexConverter(_MyEnum.values);
+  const values = {_MyEnum.one: 0, _MyEnum.two: 1, _MyEnum.three: 2, null: null};
+
+  group('encodes', () {
+    values.forEach((key, value) {
+      test('$key as $value', () => expect(converter.mapToSql(key), value));
+    });
+  });
+
+  group('decodes', () {
+    values.forEach((key, value) {
+      test('$key as $value', () => expect(converter.mapToDart(value), key));
+    });
+  });
+}