Set the property `avg_Rossby` explicitly to 0

The vertex property `avg_Rossby` was never set after `n_valid_Rossby ==
0`. It appears that it had then a default value of 0. Better to
explicitly set it to 0.

cost_function.py

@@ -61,11 +61,7 @@ def calculate_radii_rossby(list_eddies, e_overestim, handlers, array_d_init):
 
     avg_rad /= len(list_eddies)
     
-    if n_valid_Rossby != 0:
-        avg_Rossby /= n_valid_Rossby
-    else:
-        avg_Rossby = None
-
+    if n_valid_Rossby != 0: avg_Rossby /= n_valid_Rossby
     return {"avg_rad": avg_rad, "avg_Rossby": avg_Rossby}
 
 def get_SHPC(array_d_ini, date_index):
@@ -170,9 +166,8 @@ for n in g.vertices():
             # Average and assign the first radii:
             g.vp.first_av_rad[n] = first_res['avg_rad']
 
-            if first_res['avg_Rossby'] is not None:
-                # Average and assign the rossbies:
-                g.vp.first_av_ros[n] = first_res['avg_Rossby']
+            # Average and assign the rossbies:
+            g.vp.first_av_ros[n] = first_res['avg_Rossby']
 
             # Last 7 days calculation:
             last_res = calculate_radii_rossby(segment[- num_of_days_to_avg:],
@@ -182,9 +177,8 @@ for n in g.vertices():
             # Average and assign the last radii
             g.vp.last_av_rad[n] = last_res['avg_rad']
 
-            if last_res['avg_Rossby'] is not None:
-                # Average and assign the rossbies:
-                g.vp.last_av_ros[n] = last_res['avg_Rossby']
+            # Average and assign the rossbies:
+            g.vp.last_av_ros[n] = last_res['avg_Rossby']
         else:
             # The number of eddies in a segment is lower than the number
             # of days over which to average. The values will be the same
@@ -192,11 +186,10 @@ for n in g.vertices():
             res = calculate_radii_rossby(segment, e_overestim, handlers,
                                          array_d_init)
 
-            if res['avg_Rossby'] is not None:
-                # Average and assign the rossbies:
-                avg_Rossby = res['avg_Rossby']
-                g.vp.first_av_ros[n] = avg_Rossby
-                g.vp.last_av_ros[n] = avg_Rossby
+            # Average and assign the rossbies:
+            avg_Rossby = res['avg_Rossby']
+            g.vp.first_av_ros[n] = avg_Rossby
+            g.vp.last_av_ros[n] = avg_Rossby
 
             # Average and assign the radii
             avg_rad = res['avg_rad']