Warning: DOMDocument::loadXML(): Empty string supplied as input

I experienced the same kind of issues. I fixed that issue by remove spacing at start of the xml file.

don't give any space at start of the xml file

<?xml version="1.0"?>
...................
..............

it should be

<?xml version="1.0"?>
...................
..............

if it is not solve your problem, show your module.xml

I found this problem when learning to build modules. Don't pre configuring the files and folder with empty .xml files, be sure to only create an .xml file with correct content and save it. Don't just leave them empty with a view of populating later as magento's error handling will just fall-over.