To reproduce:
1. Open attached project
2. Press play
3. Observe Console window

Expected: 'URL NULL" and "string NULL" printed out to console - both variables correctly assigned as null
Actual: 'URL NULL" not printed out to console - VideoPlayer.url is allowed to be null but is not recognized as such (picture VPDebug.png)

Reproduced in: 5.6.1p4, 2017.1.0b10, 2017.2.0a4

Note: suggestion would be to either forbid url to be null or fix the variable to be recognized as one
Note: check picture code.png to get familiar with used testing code
Note: VideoPlayer did not exist in earlier versions