add error handling

Author: AtsushiSakai

PathPlanning/RRTStarDubins/rrt_star_dubins.py

@@ -66,6 +66,10 @@ def Planning(self, animation=True):
         # generate coruse
         lastIndex = self.get_best_last_index()
         #  print(lastIndex)
+
+        if lastIndex is None:
+            return None
+
         path = self.gen_final_course(lastIndex)
         return path