Allow list values to be null when parsing

csharp/src/Google.Protobuf.Test/JsonParserTest.cs

@@ -695,6 +695,22 @@ namespace Google.Protobuf
             Assert.AreEqual(Value.ForList(Value.ForNumber(1), Value.ForString("x")), Value.Parser.ParseJson("[1, \"x\"]"));
         }
 
+        [Test]
+        public void Value_List_WithNullElement()
+        {
+            var expected = Value.ForList(Value.ForString("x"), Value.ForNull(), Value.ForString("y"));
+            var actual = Value.Parser.ParseJson("[\"x\", null, \"y\"]");
+            Assert.AreEqual(expected, actual);
+        }
+
+        [Test]
+        public void StructValue_NullElement()
+        {
+            var expected = Value.ForStruct(new Struct { Fields = { { "x", Value.ForNull() } } });
+            var actual = Value.Parser.ParseJson("{ \"x\": null }");
+            Assert.AreEqual(expected, actual);
+        }
+
         [Test]
         public void ParseListValue()
         {

csharp/src/Google.Protobuf/JsonParser.cs

@@ -264,11 +264,12 @@ namespace Google.Protobuf
                     return;
                 }
                 tokenizer.PushBack(token);
-                if (token.Type == JsonToken.TokenType.Null)
+                object value = ParseSingleValue(field, tokenizer);
+                if (value == null)
                 {
                     throw new InvalidProtocolBufferException("Repeated field elements cannot be null");
                 }
-                list.Add(ParseSingleValue(field, tokenizer));
+                list.Add(value);
             }
         }