Fix parsing of broken entity references (invalid numbers).

lib/src/xml/entities/default_mapping.dart

@@ -27,10 +27,12 @@ class XmlDefaultEntityMapping extends XmlEntityMapping {
     if (input.length > 1 && input[0] == '#') {
       if (input.length > 2 && (input[1] == 'x' || input[1] == 'X')) {
         // Hexadecimal character reference.
-        return String.fromCharCode(int.parse(input.substring(2), radix: 16));
+        final value = int.tryParse(input.substring(2), radix: 16);
+        return value != null ? String.fromCharCode(value) : null;
       } else {
         // Decimal character reference.
-        return String.fromCharCode(int.parse(input.substring(1)));
+        final value = int.tryParse(input.substring(1));
+        return value != null ? String.fromCharCode(value) : null;
       }
     } else {
       // Named character reference.

test/entity_test.dart

@@ -2,11 +2,6 @@ import 'package:test/test.dart';
 import 'package:xml/src/xml/utils/character_data_parser.dart';
 import 'package:xml/xml.dart';
 
-void expectDecode(XmlEntityMapping mapping, String input, String output) {
-  final entityText = mapping.decode(input);
-  expect(entityText, output, reason: 'entity decoding');
-}
-
 void testDefaultMapping(XmlEntityMapping entityMapping) {
   group('decode', () {
     test('&#xHHHH;', () {
@@ -27,7 +22,10 @@ void testDefaultMapping(XmlEntityMapping entityMapping) {
       expect(entityMapping.decode('"'), '"');
     });
     test('invalid', () {
-      expect(entityMapping.decode('&invalid;'), '&invalid;');
+      expect(entityMapping.decode('&Invalid;'), '&Invalid;');
+      expect(entityMapping.decode('&#Invalid;'), '&#Invalid;');
+      expect(entityMapping.decode('&#xInvalid;'), '&#xInvalid;');
+      expect(entityMapping.decode('&#XInvalid;'), '&#XInvalid;');
     });
     test('incomplete', () {
       expect(entityMapping.decode('&'), '&');
@@ -153,35 +151,35 @@ void main() {
     const entityMapping = XmlDefaultEntityMapping.html();
     testDefaultMapping(entityMapping);
     test('special', () {
-      expectDecode(entityMapping, 'é', 'é');
-      expectDecode(entityMapping, 'É', 'É');
+      expect(entityMapping.decode('é'), 'é');
+      expect(entityMapping.decode('É'), 'É');
     });
   });
   group('html5', () {
     const entityMapping = XmlDefaultEntityMapping.html5();
     testDefaultMapping(entityMapping);
     test('special', () {
-      expectDecode(entityMapping, '★', '★');
-      expectDecode(entityMapping, '█', '█');
+      expect(entityMapping.decode('★'), '★');
+      expect(entityMapping.decode('█'), '█');
     });
   });
   group('null', () {
     const entityMapping = XmlNullEntityMapping();
     group('decode', () {
       test('entities', () {
-        expectDecode(entityMapping, 'A', 'A');
-        expectDecode(entityMapping, 'A', 'A');
-        expectDecode(entityMapping, '&', '&');
+        expect(entityMapping.decode('A'), 'A');
+        expect(entityMapping.decode('A'), 'A');
+        expect(entityMapping.decode('&'), '&');
       });
       test('invalid entities', () {
-        expectDecode(entityMapping, '&;', '&;');
-        expectDecode(entityMapping, '&invalid;', '&invalid;');
-        expectDecode(entityMapping, '&incomplete', '&incomplete');
+        expect(entityMapping.decode('&;'), '&;');
+        expect(entityMapping.decode('&invalid;'), '&invalid;');
+        expect(entityMapping.decode('&incomplete'), '&incomplete');
       });
       test('combinations', () {
-        expectDecode(entityMapping, 'a&b', 'a&b');
-        expectDecode(entityMapping, '&x&', '&x&');
-        expectDecode(entityMapping, '&&', '&&');
+        expect(entityMapping.decode('a&b'), 'a&b');
+        expect(entityMapping.decode('&x&'), '&x&');
+        expect(entityMapping.decode('&&'), '&&');
       });
     });
     group('encode', () {