There is an issue navigating between Xray issues

when navigating through Test Sets and Tests a blank page will be displayed

How to reproduce:

Step	Result
From a Test Set issue, navigate to an associated Test, make sure that the project side bar is present	Test issue is displayed
navigate back to the Test Set issue using the go back button of the browser	Test Set issue is displayed
navigate back to the same Test by clicking the Test link	A blank page will be displyed. There is a javascript error.

The opposite also occurs (navigating from Tests to Test Sets) and might potentially occur where datatables are being used.

Note: this was reproduced in JIRA 7.12.1 and do not seem to occur in older versions (ex: JIRA 7.3.3)