if no sidewalks or crosswalks, return empty geodataframes

src/tile2net/raster/pednet.py

@@ -1,6 +1,7 @@
 import logging
 import datetime
 import shutil
+import warnings
 
 import pandas as pd
 import os
@@ -217,6 +218,11 @@ def create_crosswalk(self):
             cw_ntw.geometry = cw_ntw.geometry.set_crs(3857)
             smoothed = wrinkle_remover(cw_ntw, 1.3)
             self.crosswalk = smoothed
+        else:
+            warnings.warn('No crosswalks found')
+            self.crosswalk = gpd.GeoDataFrame({
+                'geometry': [],
+            },crs=3857)
 
     def create_lines(self, gdf: gpd.GeoDataFrame) -> gpd.GeoDataFrame:
         """
@@ -322,6 +328,11 @@ def create_sidewalks(self):
             except:
                 # logging.info('cannot save modified')
                 self.sidewalk = sw_uni_lines
+        else:
+            warnings.warn('No sidewalk polygons found')
+            self.sidewalk = gpd.GeoDataFrame({
+                'geometry': [],
+            }, crs=3857)
 
         self.sidewalk['f_type'] = 'sidewalk'