SQL Server NULL Index I am new here and have a little question.

In a customer environment after checking his index fragmentation we see some "NULL" named index that we couldn't rebuilt or reorganize.

This was a SQL Server 2008 R2 Sp1. I have try looking on the net for this unnamed index but have no luck finding anything about it, can anyone please enlighten me on what are those.
These "indexes" are actually not indexes at all. They're called heaps, which is an internal structure that holds the table data without using any ordering mechanism like an index does.

Since there's no order, there's nothing to do as far as reorganizing or rebuilding goes, so these can be safely ignored as far as consideration for index maintenance. I would recommend using a 3rd-party solution for index maintenance though.

If you're new to index structures in SQL Server, I have a video here that explains them.