Null pointer error (or infinite waiting) when cannot connect to DB

[joohokim1]

Describe the bug
I saw null pointer exception when I tried to load a W.DS based on a database type I.DS.
Moreover, if I try to clone it, the waiting does not end.

To Reproduce
Steps to reproduce the behavior:

1. Check the database connection is healty.
2. Import & wrangle a table.
3. Turn off the DBMS.
4. Load the W.DS. (restarting might be needed)
5. Or clone the W.DS.

Expected behavior
Null pointer exception and infinite waiting should be changed into showing a proper error message, like "Cannot connect the DB" or "Check the connection to DB."

Screenshots

Desktop (please complete the following information):

• OS: MacOS
• Browser: Chrome
• Version: 68.0.3440.106

Additional context
As you can see the screenshot above, the browser gets 500 before the inifite loop.

[kaypark-skt]

Not reproduced

[joohokim1]

Do not need to test more. It's probably caused by temporary state of F/E pages.