Hub UI displays does not check if hub URL is empty
The UI can take in multiple Hub urls separated by `` and each Hub will be displayed as a separate tab in the UI. If the config has a trailing `` this will result in an empty string after the UI splits the urls and it will display a "hidden" tab that will fail to load anything (see image below)
Steps to reproduce:
1. Edit the `market.base.urls` property in cdap-site to something like : `www.example.com+`
2. Open the CDAP UI and click on Hub. If you click just to the right of the default hub you will notice there is an empty tab.
Fixed small bug in Hub UI when using multiple hubs