Changing name of folder in Rails - Git won't let me add to commit

Referencing the screenshot above, I changed the name of the lowest-level folder in the tree. For example, I changed "Chips" to "chips." Oddly, Git refuses to recognize the following command when I try to add it to the commit:

git add public/images/chips/

The only way I can get it to add the file to the commit is by adding an actual file in the subfolder.

Any ideas how to handle?