Avoid NullReferenceException when accessing CustomOptions

Even though the property is deprecated, it still shouldn't throw.

csharp/src/Google.Protobuf.Test/Reflection/CustomOptionsTest.cs

@@ -41,6 +41,7 @@ using static Google.Protobuf.WireFormat;
 using static UnitTest.Issues.TestProtos.ComplexOptionType2.Types;
 using static UnitTest.Issues.TestProtos.UnittestCustomOptionsProto3Extensions;
 using static UnitTest.Issues.TestProtos.DummyMessageContainingEnum.Types;
+using Google.Protobuf.TestProtos;
 
 #pragma warning disable CS0618
 
@@ -177,6 +178,21 @@ namespace Google.Protobuf.Test.Reflection
             AssertOption(new Aggregate { S = "FieldAnnotation" }, fieldOptions.TryGetMessage, Fieldopt, AggregateMessage.Descriptor.Fields["fieldname"].GetOption);
         }
 
+        [Test]
+        public void NoOptions()
+        {
+            var fileDescriptor = UnittestProto3Reflection.Descriptor;
+            var messageDescriptor = TestAllTypes.Descriptor;
+            Assert.NotNull(fileDescriptor.CustomOptions);
+            Assert.NotNull(messageDescriptor.CustomOptions);
+            Assert.NotNull(messageDescriptor.Fields[1].CustomOptions);
+            Assert.NotNull(fileDescriptor.Services[0].CustomOptions);
+            Assert.NotNull(fileDescriptor.Services[0].Methods[0].CustomOptions);
+            Assert.NotNull(fileDescriptor.EnumTypes[0].CustomOptions);
+            Assert.NotNull(fileDescriptor.EnumTypes[0].Values[0].CustomOptions);
+            Assert.NotNull(TestAllTypes.Descriptor.Oneofs[0].CustomOptions);
+        }
+
         private void AssertOption<T, D>(T expected, OptionFetcher<T> fetcher, Extension<D, T> extension, Func<Extension<D, T>, T> descriptorOptionFetcher) where D : IExtendableMessage<D>
         {
             T customOptionsValue;

csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs

@@ -129,7 +129,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this enum.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value enum option for this descriptor

csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs

@@ -74,7 +74,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this enum value.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value enum value option for this descriptor

csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs

@@ -299,7 +299,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this field.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value field option for this descriptor

csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs

@@ -542,7 +542,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this file.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value file option for this descriptor

csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs

@@ -261,7 +261,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this message.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value message option for this descriptor

csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs

@@ -74,7 +74,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this method.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value method option for this descriptor

csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs

@@ -106,7 +106,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this oneof.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value oneof option for this descriptor

csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs

@@ -95,7 +95,7 @@ namespace Google.Protobuf.Reflection
         /// The (possibly empty) set of custom options for this service.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use GetOption")]
-        public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// Gets a single value service option for this descriptor