Windows version : java.lang.NullPointerException at com.google.refine.io.FileProjectManager.saveToFile(FileProjectManager.java:316)

Describe the bug
At the creation of a new project on CSV file, after the preview, there is no more than a running logo on the navigator.

To Reproduce
Steps to reproduce the behavior:

1. create a new flat file project. (I tried a small file to control if it could be a memory problem but that is not the case).
2. pass the preview.
3. See nothing more on the navigator and the regular message into the console running the web server :
   java.lang.NullPointerException
   at com.google.refine.io.FileProjectManager.saveToFile(FileProjectManager.java:316)
   at com.google.refine.io.FileProjectManager.saveWorkspace(FileProjectManager.java:272)
   at com.google.refine.ProjectManager.save(ProjectManager.java:232)
   at com.google.refine.RefineServlet$AutoSaveTimerTask.run(RefineServlet.java:92)
   at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
   at java.util.concurrent.FutureTask.runAndReset(Unknown Source)
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(Unknown Source)
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
   at java.lang.Thread.run(Unknown Source)
   17:03:58.808 [ FileProjectManager] Failed to save workspace (15ms)

Desktop (please complete the following information):

• OS: Windows server 2016

OpenRefine (please complete the following information):

• OR 3.0-rc1

Additional context
It does not come from the data. with a simpler text file, it is not working too.

Start with FileProjectManager.java at saveToFile line 316 and trace the workspace save call from ProjectManager.java and RefineServlet.java. Reproduce project creation from a small CSV or text file on Windows Server 2016, then verify that passing the preview completes without the navigator hanging or the NullPointerException during autosave.