Handle NOT_FOUND addresses in Distance Matrix API responses (closes #124)

lib/src/distance.dart

@@ -303,13 +303,13 @@ class Row {
 
 @JsonSerializable()
 class Element {
-  final Value distance;
-  final Value duration;
+  final Value? distance;
+  final Value? duration;
   final String? elementStatus;
 
   Element({
-    required this.distance,
-    required this.duration,
+    this.distance,
+    this.duration,
     this.elementStatus,
   });
 

test/distance_test.dart

@@ -493,12 +493,28 @@ Future<void> main() async {
         expect(response.destinationAddresses.first,
             equals('Rd 11, Dhaka 1212, Bangladesh'));
         expect(response.rows.first.elements, hasLength(1));
-        expect(response.rows.first.elements.first.duration.text,
+        expect(response.rows.first.elements.first.duration?.text,
             equals('29 mins'));
-        expect(response.rows.first.elements.first.duration.value, equals(1725));
+        expect(response.rows.first.elements.first.duration?.value, equals(1725));
         expect(
-            response.rows.first.elements.first.distance.text, equals('9.2 km'));
-        expect(response.rows.first.elements.first.distance.value, equals(9247));
+            response.rows.first.elements.first.distance?.text, equals('9.2 km'));
+        expect(response.rows.first.elements.first.distance?.value, equals(9247));
+      });
+
+      test('decode NOT_FOUND response', () {
+        var response = DistanceResponse.fromJson(_notFoundResponseExample);
+
+        expect(response.isOkay, isTrue);
+        expect(response.rows, hasLength(1));
+        expect(response.originAddresses, hasLength(1));
+        expect(response.originAddresses.first,
+            equals('Bakshi Bazar Road, Dhaka, Bangladesh'));
+        expect(response.destinationAddresses, hasLength(1));
+        expect(response.destinationAddresses.first,
+            equals(''));
+        expect(response.rows.first.elements, hasLength(1));
+        expect(response.rows.first.elements.first.duration, null);
+        expect(response.rows.first.elements.first.distance, null);
       });
     });
   });
@@ -520,3 +536,18 @@ final _responseExample = {
   ],
   'status': 'OK'
 };
+
+final _notFoundResponseExample = {
+  'destination_addresses': [''],
+  'origin_addresses': ['Bakshi Bazar Road, Dhaka, Bangladesh'],
+  'rows': [
+    {
+      'elements': [
+        {
+          'status': 'NOT_FOUND'
+        }
+      ]
+    }
+  ],
+  'status': 'OK'
+};