source map is always empty

[villander]

my machine

ember-cli: 3.3.0
node: 8.11.4
os: darwin x64

I'm using this plugin, but the source maps read is always empty. the problem happens on _readSourceMap function

|    - Uploading sourcemaps to Rollbar
|    - Uploading sourcemap to Rollbar: version= name=https://my.paycertify.com/assets/auto-import-fastboot-e289ea484a4d8949ea84cb262a624452.js file=tmp/deploy-dist/assets/auto-import-fastboot-81f919f3d82c38703c7b0de8c4c4a874.map
|    - Uploading sourcemap to Rollbar: version= name=https://my.paycertify.com/assets/vendor-9a51012fdf0474b17c5760686fdd3586.js file=tmp/deploy-dist/assets/vendor-534fce18d47740d0e26096c68734a690.map
|    - Uploading sourcemap to Rollbar: version= name=https://my.paycertify.com/assets/web-app-053d567f210ca3099a95b2ad14d9aa8e.js file=tmp/deploy-dist/assets/web-app-12465c4e2bb0e4ec3979d1019af914cf.map
|
+- didFail
StatusCodeError: 400 - "{\"code\":400,\"type\":\"Bad Request\",\"message\":\"sourcemap: mappings are empty\"}"
StatusCodeError: 400 - "{\"code\":400,\"type\":\"Bad Request\",\"message\":\"sourcemap: mappings are empty\"}"

https://github.com/bgentry/ember-cli-deploy-rollbar-sourcemap/blob/master/index.js#L115-L129