Version 10.2 rasters says Raster.path
is the "full path and filename".
It's just the path.
You need to do os.path.join(raster.path, raster.name)
to get actually get the full path.
[Version Pro and earlier toolboxes] (https://pro.arcgis.com/en/pro-app/arcpy/classes/parameter.htm) claimed that you set the parameter dependendencies with a list of integers. This is incorrect. You need to use either a list of integers as strings or the parameter names.
The example dataset for the flow accumulation function is wrong.