Ember build for production failed - Unexpected character '#'... how can I find it?

Question

When I ember build or ember server, no issues.

When I try to ember build --environment=production, I get this:

version: 0.2.0
Build failed.
Unexpected character '#'
Error
    at new JS_Parse_Error (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/lib/parse.js:196:18)
    at js_error (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/lib/parse.js:204:11)
    at parse_error (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/lib/parse.js:313:55)
    at Object.next_token [as input] (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/lib/parse.js:561:9)
    at next (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/lib/parse.js:660:25)
    at Object.parse (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/lib/parse.js:646:15)
    at APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:82:33
    at Array.forEach (native)
    at Object.exports.minify (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:77:15)
    at UglifyWriter.processFile (APP_FOLDER/node_modules/ember-cli-uglify/node_modules/broccoli-uglify-sourcemap/index.js:98:25)

How can I find where this unexpected # is?