Prohibit null values in repeated and map fields in JSON

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

@@ -170,6 +170,36 @@ namespace Google.Protobuf
             AssertRoundtrip(message);
         }
 
+        [Test]
+        public void RepeatedField_NullElementProhibited()
+        {
+            string json = "{ \"repeated_foreign_message\": [null] }";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void RepeatedField_NullOverallValueAllowed()
+        {
+            string json = "{ \"repeated_foreign_message\": null }";
+            Assert.AreEqual(new TestAllTypes(), TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("{ \"mapInt32Int32\": { \"10\": null }")]
+        [TestCase("{ \"mapStringString\": { \"abc\": null }")]
+        [TestCase("{ \"mapInt32ForeignMessage\": { \"10\": null }")]
+        public void MapField_NullValueProhibited(string json)
+        {
+            Assert.Throws<InvalidProtocolBufferException>(() => TestMap.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void MapField_NullOverallValueAllowed()
+        {
+            string json = "{ \"mapInt32Int32\": null }";
+            Assert.AreEqual(new TestMap(), TestMap.Parser.ParseJson(json));
+        }
+
         [Test]
         public void IndividualWrapperTypes()
         {

csharp/src/Google.Protobuf/JsonParser.cs

@@ -239,6 +239,10 @@ namespace Google.Protobuf
                     return;
                 }
                 tokenizer.PushBack(token);
+                if (token.Type == JsonToken.TokenType.Null)
+                {
+                    throw new InvalidProtocolBufferException("Repeated field elements cannot be null");
+                }
                 list.Add(ParseSingleValue(field, tokenizer));
             }
         }
@@ -270,7 +274,10 @@ namespace Google.Protobuf
                 }
                 object key = ParseMapKey(keyField, token.StringValue);
                 object value = ParseSingleValue(valueField, tokenizer);
-                // TODO: Null handling
+                if (value == null)
+                {
+                    throw new InvalidProtocolBufferException("Map values must not be null");
+                }
                 dictionary[key] = value;
             }
         }