(fix #369)

tensorpack/graph_builder/model_desc.py

@@ -147,7 +147,7 @@ class ModelDesc(ModelDescBase):
         """
         cost = self._get_cost()
         reg_cost = regularize_cost_from_collection()
-        if reg_cost:
+        if reg_cost is not None:
             return tf.add(cost, reg_cost, name='cost_with_regularizer')
         else:
             return cost

tensorpack/models/regularize.py

@@ -64,7 +64,7 @@ def regularize_cost_from_collection(name='regularize_cost'):
     In replicated mode, will only regularize variables within the current tower.
 
     Returns:
-        a scalar tensor, the regularization loss, or 0
+        a scalar tensor, the regularization loss, or None
     """
     regularization_losses = set(tf.get_collection(tf.GraphKeys.REGULARIZATION_LOSSES))
     ctx = get_current_tower_context()
@@ -77,7 +77,7 @@ def regularize_cost_from_collection(name='regularize_cost'):
         reg_loss = tf.add_n(list(regularization_losses), name=name)
         return reg_loss
     else:
-        return 0
+        return None
 
 
 @layer_register(log_shape=False, use_scope=False)