Property is NULL?

[mac]

Somehow I found I have some data are categorized as "NULL" property by checking it in the admin console, Datastore Statistics (As attached image).

And the size is 119MBytes.

And I found one of my model have duplicated properties, for example.

comment  Text 780 Bytes (0% of the entity)

comment  NULL 8 MBytes (1% of the entity)

There are about 20 duplicated properties.

Does anyone know why these properties are created? And how could I remove them(w/o touching the non-null one)?

Thanks.

[mac]

I think I need to change the title. When I mentioned the NULL in the last thread. I mean the Property type is NULL, not the content of that property is NULL. That's quite odd to me.