diff --git a/urbantrips/viz/viz.py b/urbantrips/viz/viz.py
index 755ec6b..0bffcb3 100644
--- a/urbantrips/viz/viz.py
+++ b/urbantrips/viz/viz.py
@@ -1438,6 +1438,9 @@ def traigo_zonificacion(viajes,
                 except KeyError:
                     matriz_order = ""
 
+                if matriz_order is None:
+                    matriz_order = ""
+
                 if var_zona in zonas.columns:
                     matriz_zonas += [[file_zona, var_zona, matriz_order]]
                     vars_zona += [var_zona]