Uncaught TypeError: Cannot read property ‘core’ of undefined

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Bug description: Uncaught TypeError: Cannot read property ‘core’ of undefined

Link to minimally-working plunker that reproduces the issue:

https://github.com/heeyoun-song/angular-sample ( 1-add-bootstrap-module )

You can fork a plunker from one of our demos and use it as a starting point.
Please note that we can not act on bug reports without a minimal reproduction scenario in plunker. Here is why:
https://github.com/ng-bootstrap/ng-bootstrap#you-think-youve-found-a-bug

Version of Angular, ng-bootstrap, and Bootstrap:

Angular:

~>>> ninezero@songhuiyun-ui-MacBook-Air ~/D/w/m/angular-sample> npm angular-cli -v
~>>> 4.2.0

ng-bootstrap:

“@ng-bootstrap/ng-bootstrap”: “^1.0.0-alpha.25”,

Bootstrap:

1) Karama Log

~>>> ninezero@songhuiyun-ui-MacBook-Air ~/D/w/m/angular-sample> karma start
01 05 2017 21:15:34.939:WARN [karma]: No captured browser, open http://localhost:9876/
01 05 2017 21:15:34.962:INFO [karma]: Karma v1.4.1 server started at http://0.0.0.0:9876/
01 05 2017 21:15:34.963:INFO [launcher]: Launching browser Chrome with unlimited concurrency
01 05 2017 21:15:34.972:INFO [launcher]: Starting browser Chrome
01 05 2017 21:15:36.633:INFO [Chrome 57.0.2987 (Mac OS X 10.12.4)]: Connected on socket CyKxHmRzOS9WVeWGAAAA with id 64103673
Chrome 57.0.2987 (Mac OS X 10.12.4) ERROR
Uncaught TypeError: Cannot read property ‘core’ of undefined
at node_modules/@ng-bootstrap/ng-bootstrap/bundles/ng-bootstrap.js:9

Chrome 57.0.2987 (Mac OS X 10.12.4) ERROR
Uncaught TypeError: Cannot read property ‘core’ of undefined
at node_modules/@ng-bootstrap/ng-bootstrap/bundles/ng-bootstrap.js:9

Chrome 57.0.2987 (Mac OS X 10.12.4): Executed 0 of 3 SUCCESS (0 secs / 0 secs)
Chrome 57.0.2987 (Mac OS X 10.12.4) ERROR
Disconnected, because no message in 10000 ms.
Chrome 57.0.2987 (Mac OS X 10.12.4): Executed 0 of 3 DISCONNECTED (10.004 secs / 0 secs)
Chrome 57.0.2987 (Mac OS X 10.12.4) ERROR
Chrome 57.0.2987 (Mac OS X 10.12.4): Executed 0 of 3 DISCONNECTED (10.004 secs / 0 secs)

2) Node version, and npm version

~>>> ninezero@songhuiyun-ui-MacBook-Air ~/D/w/m/angular-sample> node –version
v7.9.0
~>>> ninezero@songhuiyun-ui-MacBook-Air ~/D/w/m/angular-sample> npm -v
4.2.0

Please let me know if you need any more information.
Error in chrome developer console starting with ng serve.