Clojurians Log v2

hi all, I have a question regarding the externs files of a library. I am interested in packaging the js-marker-clusterer library from google and I noticed that the source file is already annotated for the closure compiler, although it does not have an externs file. In case the annotation already exists, do I still need to create the externs file?

library code: https://raw.githubusercontent.com/googlemaps/js-marker-clusterer/gh-pages/src/markerclusterer.js