Need to properly handle null for blob container names

[jcookems]

When null is passed as the container name in the Blob service APIs, it maps to the container named "null", which is not the intended behavior. It should throw an exception, or interpret null as the root container (which would be consistent with passing the empty string, see issue #82).

[gcheng]

I think this should be fixed with unit test(s). root container is an important scenario to support.

[joostdenijs]

null value should go to root (same as empty string)

[gcheng]

It depends on the method, for create container, it doesn't make sense to send the create container request because the root container is already there.

[joostdenijs]

I think that null should be the root container everywhere, and in the case of create container, the request to create the root container will fail server side.

[gcheng]

also for delete container, if we do not curb the request on client side, an incorrect delete container may delete the whole account in future.

[gcheng]

fix ready.

[gcheng]

actually, no, it is more complicated than it looks like.

http://msdn.microsoft.com/en-us/library/windowsazure/ee395424.aspx

[gcheng]

To list the blobs in the root container:
GET http://myaccount.blob.core.windows.net/$root?restype=container&comp=list

To delete the root container:
DELETE http://myaccount.blob.core.windows.net/$root?restype=container

Missed from documentation, I guess creating a root container should be

PUT http://myaccount.blob.core.windows.net/$root?restype=container

[gcheng]

actually, if we always specify the root container as $root, the amount code change seems to be minimum.