WARNING: Category '' in library *any library* is not valid. Setting to 'Uncategorized'
Edit or add library.properties to that folder so that you specify a valid category. 

Example of library.properties:

name=WebServer
version=1.0
author=Cristian Maglie &lt;c.maglie@example.com&gt;, Pippo Pluto &lt;pippo@example.com&gt;
maintainer=Cristian Maglie &lt;c.maglie@example.com&gt;
sentence=A library that makes coding a Webserver a breeze.
paragraph=Supports HTTP1.1 and you can do GET and POST.
category=Communication
url=http://example.com/
architectures=avr