ionic-cli/node.js server incurs 404 when requesting .map files

Whenever I use ionic-cli launch a server (I suspect it is node.js server) to test my ionic application, anytime when the .map file is requested, the server would return a 404 status. The .map file is the source map generated from SASS or TypeScript, and they are good time safer for code debugging. Anyone knows of a way to make the server serve .map files correctly?