Fix async GetRowVersionAsync as well

Author: mythz

src/ServiceStack.OrmLite/Async/OrmLiteWriteCommandExtensionsAsync.cs

@@ -633,7 +633,7 @@ internal static async Task<object> GetRowVersionAsync(this IDbCommand dbCmd, Mod
             if (to is ulong u && modelDef.RowVersion.ColumnType == typeof(byte[]))
                 return BitConverter.GetBytes(u);
 
-            return to;
+            return to ?? modelDef.RowVersion.ColumnType.GetDefaultValue();
         }
     }
 }

tests/ServiceStack.OrmLite.Tests/RowVersionTests.cs

@@ -261,6 +261,24 @@ public void Can_Save_ModelWithAutoGuidAndRowVersion()
             Assert.That(dbRow.Name, Is.EqualTo("B"));
         }
 
+        [Test]
+        public async Task Can_Save_ModelWithAutoGuidAndRowVersion_Async()
+        {
+            db.DropAndCreateTable<ModelWithAutoGuidAndRowVersion>();
+            var row = new ModelWithAutoGuidAndRowVersion { Name = "A" };
+            
+            Assert.That(await db.SaveAsync(row));
+
+            var dbRow = await db.SingleByIdAsync<ModelWithAutoGuidAndRowVersion>(row.Id);
+            Assert.That(dbRow.Name, Is.EqualTo(row.Name));
+
+            dbRow.Name = "B";
+            await db.SaveAsync(dbRow);
+
+            dbRow = await db.SingleByIdAsync<ModelWithAutoGuidAndRowVersion>(row.Id);
+            Assert.That(dbRow.Name, Is.EqualTo("B"));
+        }
+
         [Test]
         public void Can_SaveAll_new_rows_and_retrieve_rowversion()
         {