[v1.8.5] TypeError - OpenNumismat\Reference\ReferenceDialog.py:254

OpenNumismat: 1.8.5
OS: Windows 10 (10.0.18362)
Python: 3.4.4 (32bit)
Qt: 5.5.1
Locale: en

Traceback (most recent call last):
File "OpenNumismat\Reference\Reference.py", line 106, in clickedButton
File "OpenNumismat\Reference\Reference.py", line 259, in _getDialog
File "OpenNumismat\Reference\ReferenceDialog.py", line 348, in __init__
File "OpenNumismat\Reference\ReferenceDialog.py", line 302, in __init__
File "OpenNumismat\Reference\ReferenceDialog.py", line 351, in _referenceWidget
File "OpenNumismat\Reference\ReferenceDialog.py", line 245, in __init__
File "OpenNumismat\Reference\ReferenceDialog.py", line 254, in currentIndexChanged
TypeError: %d format: a number is required, not NoneType

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This error appeared when I was adding a new coin and selected region Europe and no country (for a Euro coin). The Unit field shows values for India coins (Rupee, Paisa, Anna), which I may have manually added, however when I am adding/editing coins from India, no values are displayed when I click the Unit field drop down (somehow the India values don't appear and when I cluck "U" to add, the Unit reference is blank and India doesn't appear as an option in the country list).