Now initializing quaternion_spline_params attribute in Segment init to None;...

Now initializing quaternion_spline_params attribute in Segment init to None; prevents errors when mapping atomic models of ssDNA

segmentmodel.py

@@ -361,9 +361,11 @@ class Segment(ConnectableElement, Group):
         a = np.array([self.start_position,self.end_position]).T
         tck, u = interpolate.splprep( a, u=[0,1], s=0, k=1)
         self.position_spline_params = tck
+        self.quaternion_spline_params = None
         
         self.sequence = None
 
+
     def clear_all(self):
         Group.clear_all(self)  # TODO: use super?
         self.beads = []
@@ -800,8 +802,6 @@ class DoubleStrandedSegment(Segment):
         self.position_spline_params = tck
         
         ## TODO: initialize sensible spline for orientation
-        self.quaternion_spline_params = None
-
 
     ## Convenience methods
     ## TODO: add errors if unrealistic connections are made