CSHARP-3703: Fix NullReferenceException when Id property has no getter. (#545)

Author: JamesKovacs

src/MongoDB.Bson/Serialization/Conventions/NamedIdMemberConvention.cs

@@ -112,7 +112,9 @@ private bool IsValidIdMember(BsonClassMap classMap, MemberInfo member)
             if (member is PropertyInfo)
             {
                 var getMethodInfo = ((PropertyInfo)member).GetMethod;
-                if (getMethodInfo.IsVirtual && getMethodInfo.GetBaseDefinition().DeclaringType != classMap.ClassType)
+                if (getMethodInfo == null ||
+                    getMethodInfo.IsVirtual &&
+                    getMethodInfo.GetBaseDefinition().DeclaringType != classMap.ClassType)
                 {
                     return false;
                 }

tests/MongoDB.Bson.Tests/Serialization/Conventions/IdMemberConventionsTests.cs

@@ -44,6 +44,14 @@ private class TestClassD
             public ObjectId _id { get; set; }
         }
 
+        private class TestClassNoIdGetter
+        {
+            public Object Id
+            {
+                set { }
+            }
+        }
+
         [Fact]
         public void TestNamedIdMemberConventionWithTestClassA()
         {
@@ -82,5 +90,14 @@ public void TestNamedIdMemberConventionWithTestClassD()
             Assert.NotNull(classMap.IdMemberMap);
             Assert.Equal("_id", classMap.IdMemberMap.MemberName);
         }
+
+        [Fact]
+        public void TestNamedIdMemberConventionWillNotReturnIdWithoutGetter()
+        {
+            var convention = new NamedIdMemberConvention("Id", "id", "_id");
+            var classMap = new BsonClassMap<TestClassNoIdGetter>();
+            convention.Apply(classMap);
+            Assert.Null(classMap.IdMemberMap);
+        }
     }
 }