TypeError: unsupported operand type(s) for -: 'QPyNullVariant' and 'long'
Traceback (most recent call last): File
"C:/Users/Erastus/.qgis2/python/pluginscontourcontour.py", line 350, in
uDataFieldUpdate self.reloadData() File
"C:/Users/Erastus/.qgis2/python/pluginscontourcontour.py", line 361, in
reloadData data=self.getData() File
"C:/Users/Erastus/.qgis2/python/pluginscontourcontour.py", line 809, in
getData self.dataChanged() File
"C:/Users/Erastus/.qgis2/python/pluginscontourcontour.py", line 706, in
dataChanged if zmax-zmin > 0: TypeError: unsupported operand type(s) for -:
'QPyNullVariant' and 'long'