Fix AsReference() in generated code for null values (#2756)

src/OrleansCodeGenerator/SerializerGenerator.cs

@@ -600,18 +600,22 @@ namespace Orleans.CodeGenerator
                         this.FieldInfo.FieldType);
 
                     // If the value is not a GrainReference, convert it to a strongly-typed GrainReference.
-                    // C#: !(value is GrainReference) ? value.AsReference<TInterface>() : value;
+                    // C#: (value == null || value is GrainReference) ? value : value.AsReference<TInterface>()
                     deepCopyValueExpression =
                         SF.ConditionalExpression(
-                            SF.PrefixUnaryExpression(
-                                SyntaxKind.LogicalNotExpression,
-                                SF.ParenthesizedExpression(
+                            SF.ParenthesizedExpression(
+                                SF.BinaryExpression(
+                                    SyntaxKind.LogicalOrExpression,
+                                    SF.BinaryExpression(
+                                        SyntaxKind.EqualsExpression,
+                                        getValueExpression,
+                                        SF.LiteralExpression(SyntaxKind.NullLiteralExpression)),
                                     SF.BinaryExpression(
                                         SyntaxKind.IsExpression,
                                         getValueExpression,
                                         typeof(GrainReference).GetTypeSyntax()))),
-                            SF.InvocationExpression(getAsReference),
-                            getValueExpression);
+                            getValueExpression,
+                            SF.InvocationExpression(getAsReference));
                 }
                 else
                 {

test/DefaultCluster.Tests/GrainReferenceTest.cs

@@ -63,6 +63,19 @@ namespace DefaultCluster.Tests.General
             g1.PassThisNested(new ChainGrainHolder { Next = g2 }).Wait();
         }
 
+        [Fact, TestCategory("BVT"), TestCategory("Functional"), TestCategory("GrainReference")]
+        public async Task GrainReference_Pass_Null()
+        {
+            IChainedGrain g1 = this.GrainFactory.GetGrain<IChainedGrain>(GetRandomGrainId());
+            IChainedGrain g2 = this.GrainFactory.GetGrain<IChainedGrain>(GetRandomGrainId());
+
+            // g1 will pass a null reference to g2
+            await g1.PassNullNested(new ChainGrainHolder { Next = g2 });
+            Assert.Null(await g2.GetNext());
+            await g1.PassNull(g2);
+            Assert.Null(await g2.GetNext());
+        }
+
         [Fact, TestCategory("BVT"), TestCategory("Functional"), TestCategory("Serialization"), TestCategory("GrainReference")]
         public void GrainReference_DotNet_Serialization()
         {

test/NonSiloTests/Serialization/BuiltInSerializerTests.cs

@@ -135,6 +135,7 @@ namespace UnitTests.Serialization
             Assert.Equal(expected.Classes[1].Interfaces[0].Int, actual.Classes[1].Interfaces[0].Int);
             Assert.Equal(0, actual.NonSerializedInt);
             Assert.Equal(expected.GetObsoleteInt(), actual.GetObsoleteInt());
+            Assert.Null(actual.SomeGrainReference);
         }
 
         [Theory, TestCategory("BVT"), TestCategory("Serialization")]
@@ -169,6 +170,7 @@ namespace UnitTests.Serialization
             Assert.Equal(expected.ReadonlyField, actual.ReadonlyField);
             Assert.Equal(expected.PublicValue, actual.PublicValue);
             Assert.Equal(expected.ValueWithPrivateSetter, actual.ValueWithPrivateSetter);
+            Assert.Null(actual.SomeGrainReference);
             Assert.Equal(expected.GetPrivateValue(), actual.GetPrivateValue());
             Assert.Equal(expected.GetValueWithPrivateGetter(), actual.GetValueWithPrivateGetter());
         }

test/TestGrainInterfaces/CodegenTestInterfaces.cs

@@ -127,6 +127,8 @@ namespace UnitTests.GrainInterfaces
         private int PrivateValue { get; set; }
         public readonly int ReadonlyField;
 
+        public IEchoGrain SomeGrainReference { get; set; }
+
         public SomeStruct(int readonlyField)
             : this()
         {
@@ -173,9 +175,10 @@ namespace UnitTests.GrainInterfaces
 
         [Obsolete("This field should be serialized")]
         public int ObsoleteInt { get; set; }
-        
 
-        #pragma warning disable 618
+        public IEchoGrain SomeGrainReference { get; set; }
+        
+#pragma warning disable 618
         public int GetObsoleteInt() => this.ObsoleteInt;
         public void SetObsoleteInt(int value)
         {

test/TestGrainInterfaces/IChainedGrain.cs

@@ -15,7 +15,9 @@ namespace UnitTests.GrainInterfaces
         //[ReadOnly]
         Task Validate(bool nextIsSet);
         Task PassThis(IChainedGrain next);
+        Task PassNull(IChainedGrain next);
         Task PassThisNested(ChainGrainHolder next);
+        Task PassNullNested(ChainGrainHolder next);
     }
     
     public class ChainGrainHolder

test/TestGrains/ChainedGrain.cs

@@ -85,11 +85,21 @@ namespace UnitTests.Grains
             return next.SetNext(this);
         }
 
+        public Task PassNull(IChainedGrain next)
+        {
+            return next.SetNext(null);
+        }
+
         public Task PassThisNested(ChainGrainHolder next)
         {
             return next.Next.SetNextNested(new ChainGrainHolder { Next = this });
         }
 
+        public Task PassNullNested(ChainGrainHolder next)
+        {
+            return next.Next.SetNextNested(new ChainGrainHolder { Next = null });
+        }
+
         #endregion
     }
 }