diff --git a/utils/data_generator.py b/utils/data_generator.py
index 046d3e8..1bde58d 100644
--- a/utils/data_generator.py
+++ b/utils/data_generator.py
@@ -207,7 +207,13 @@ def transform(self, x):
         Use the calculated scalar to transform data.
         """
 
-        return (x - self.mean) / self.std
+        # the numpy contain zero, 
+        # dividing zero gives NAN, which break the code
+        # return (x - self.mean) / self.std
+        x = (x - self.mean) / self.std
+        x[np.isnan(x)] = 0
+
+        return x
 
     def generate_train(self):
         """Generate batch data for training.
@@ -353,7 +359,14 @@ def transform(self, x):
         Use the calculated scalar to transform data.
         """
 
-        return (x - self.mean) / self.std
+        # return (x - self.mean) / self.std
+        # the numpy contain zero, 
+        # dividing zero gives NAN, which break the code
+        # return (x - self.mean) / self.std
+        x = (x - self.mean) / self.std
+        x[np.isnan(x)] = 0
+
+        return x
 
     def generate_eval(self):
         """