Latest version. Both Windows and Linux.

Reproduce:

1. Select entry without DOI
2. Click "Look for DOI" (running the Swedish translation...)
3. Click "Get information from DOI"
   NPE

Resolved by clicking in the DOI text field. After that, no NPE. However, it seems like one will need to save (or at least do something more) to actually get the additional information when one clicks.

BTW, the "Look for DOI"-functionality is brilliant!