Avoid duplicating values in JSON for deserialization

Author: kzu

src/TableStorage/TableRepository`1.cs

@@ -193,13 +193,13 @@ T ToEntity(TableEntity entity)
             // perform its advanced ctor and conversion detection as usual.
             writer.WriteStartObject();
 
-            if (partitionKeyProperty != null)
+            if (partitionKeyProperty != null && !entity.ContainsKey(partitionKeyProperty))
                 writer.WriteString(partitionKeyProperty, entity.PartitionKey);
 
-            if (rowKeyProperty != null)
+            if (rowKeyProperty != null && !entity.ContainsKey(rowKeyProperty))
                 writer.WriteString(rowKeyProperty, entity.RowKey);
 
-            if (entity.Timestamp != null)
+            if (entity.Timestamp != null && !entity.ContainsKey(nameof(ITableEntity.Timestamp)))
                 writer.WriteString(nameof(ITableEntity.Timestamp), entity.Timestamp.Value.ToString("O"));
 
             foreach (var property in entity)