minor

modules/amv/intercompare.py

@@ -124,7 +124,7 @@ def filter_amvs(amvs, qi=None, cqi=50, qif=None, lat_range=None):
     if lat_range is not None:
         keep = np.logical_and(amvs[:, amv_lat_idx] > lat_range[0], amvs[:, amv_lat_idx] < lat_range[1])
         if np.sum(keep) == 0:
-            return
+            return None
         amvs = amvs[keep, :]
 
     if cqi is None: