Nightly Serial is broken

Using: arduino-nightly-windows_19 July 2017 5_34_36
Windows 7 x86

Serial throws a null pointer exception when opening the serial monitor.
I believe this [commit](https://github.com/arduino/Arduino/commit/125846f55d624951897d5a432e528e9cc7a5e06f) caused this.

Using the arduino-core.jar from the official release (arduino-1.8.3-windows) resolves this.