adding undefined check, in case of reference curve it might be null.

[vibhaMalviya]

Pull Request

Hi,

Thanks for helping us improve the Predix UI platform by submitting a Pull Request.

To help us merge your Pull Request as fast as possible, please fill out the following sections:

• A description of the changes proposed in the pull request:

• A reference to a related issue (if applicable):

• @mentions of the person or team responsible for reviewing proposed changes:

• working tests:

  The tests need to be functional and/or unit tests, written for the wct framework, and placed in the test folder, following our testing guidelines.