diff --git a/behaviors/custom/Dribble/Dribble.py b/behaviors/custom/Dribble/Dribble.py
index cbd327e..bc2aa01 100644
--- a/behaviors/custom/Dribble/Dribble.py
+++ b/behaviors/custom/Dribble/Dribble.py
@@ -208,7 +208,8 @@ class Dribble():
             if self.phase >= WIND_DOWN_STEPS - 5:
                 self.phase = 0
                 return True
-        np.array(self.gather_expert_data.append((self.obs, self.act)), dtype=object)
+        if self.obs != None and self.act != None:
+            np.array(self.gather_expert_data.append((self.obs, self.act)), dtype=object)
         size = len(self.gather_expert_data)
         if size > 5e4:
             np.save('/home/apollo3d/code/TEST_Dribble/behaviors/custom/Dribble/expert_data.npy', self.gather_expert_data)