Error running BAL toolbox ArcGIS10.5 about bal HOT 1 OPEN

Appears to be the way 10.5 handles the arcpy.Describe().extent attribute. If this option is set to "Default", "Union of Inputs" or "Intersection of Inputs", then 10.5 returns "None". If the extent is specified manually, or a dataset is selected, then the tool executes as expected.

in bal.py l247, I added `arcpy.AddMessage("Extent: %s"%repr(extent_list))

On ArcGIS 10.5, using "Default" option for Extent:

Running script BAL...
DEM's spatial reference type is Projected
Get the area of interest from the input extent ...
Extent: ['None']
Failed script BAL...

Traceback (most recent call last):
File "C:\Users\u12161\Downloads\BAL\BAL-master\bal.py", line 371, in
run()
File "C:\Users\u12161\Downloads\BAL\BAL-master\bal.py", line 357, in run
mask = find_aoi(extent, dem, veg)
File "C:\Users\u12161\Downloads\BAL\BAL-master\bal.py", line 317, in find_aoi
get_extent_mask(extent, mask)
File "C:\Users\u12161\Downloads\BAL\BAL-master\bal.py", line 247, in get_extent_mask
array.add(arcpy.Point(float(extent_list[0]), float(extent_list[1])))
ValueError: could not convert string to float: None

On ArcGIS 10.3:

Running script BAL...
DEM's spatial reference type is Projected
Get the area of interest from the input extent ...
Extent: ['717363.28258812', '6190392.84914239', '719513.28258812', '6192167.84914239', 'NaN', 'NaN', 'NaN', 'NaN']
...

Temporary fix

Set the extent option, either by specifying a raster to match the extent of, or selecting "As specified below" and entering values in the four entry boxes.

from bal.