Fixed small bug introduced in 64462997

mrdna/segmentmodel.py

@@ -727,7 +727,11 @@ class Segment(ConnectableElement, Group):
         if nt_pos >= 0 and nt_pos < self.num_nt:
             return (self,nt_pos,is_fwd)
         else:
-            c,A,B = self.get_contour_sorted_connections_and_locations(type_='intrahelical')[0 if nt_pos < 0 else -1]
+            try:
+                c,A,B = self.get_contour_sorted_connections_and_locations(type_='intrahelical')[0 if nt_pos < 0 else -1]
+            except:
+                return None
+
             ## Special logic for circular segments
             assert(A.container == self)
             if A.container == B.container: