get repositoryUrls() -> this.items is undefined

[mariannafld]

Dear pleerock,

I'm a newbie in angular 2 and in typescript, and I have a question regarding using class-transformer package.
Running this example, I have an exception when calling to repositoryResult.repositoryUrls.
The exception is: ERROR in Cannot read property 'map' of undefined.
What can be reason of this exception?

Thank you in advance