Small fix for 422f772c4

src/blenderbim/blenderbim/tool/geometry.py

@@ -402,6 +402,8 @@ class Geometry(blenderbim.core.tool.Geometry):
             return styles
 
         usage_count = [0] * len(obj.material_slots)
+        if not usage_count: # if there are no materials, polygons will still use index 0
+            return []
         for poly in obj.data.polygons:
             usage_count[poly.material_index] += 1
         styles = [style for style, usage in zip(styles, usage_count, strict=True) if usage > 0]