git checkout fail because of new submodule

While on development branch I am trying to do:

git checkout master

And getting the message:

error: The following untracked working tree files would be overwritten
by checkout:

And it points me to a directory.

The problem is that I made this directory to be submodule. But its not a submodule in master, so it tells me that those files will be override and aborting the checkout.

What can I do?

Git Baby is a git and github fan, let's start git clone.