diff --git a/alf/algorithms/merlin_algorithm.py b/alf/algorithms/merlin_algorithm.py
index 4f3492442..d121b11e2 100644
--- a/alf/algorithms/merlin_algorithm.py
+++ b/alf/algorithms/merlin_algorithm.py
@@ -543,6 +543,8 @@ def __init__(self,
             enc_layers.append(res_block)
             in_channels = 64
 
+        if output_activation is None:
+            output_activation = alf.math.identity
         enc_layers.extend([
             nn.Flatten(),
             alf.layers.FC(
diff --git a/alf/config_util.py b/alf/config_util.py
index 6eccaf5fe..267f58986 100644
--- a/alf/config_util.py
+++ b/alf/config_util.py
@@ -337,7 +337,11 @@ def pre_config(configs):
         try:
             config1(name, value, mutable=False)
             _HANDLED_PRE_CONFIGS.append((name, value))
-        except ValueError:
+        except ValueError as e:
+            # Most of the times, for command line flags, this warning is a false alarm.
+            # This can be useful in other failures, e.g. when the Config has already been used,
+            # before configuring its value.
+            logging.warning("pre_config potential error: %s", e)
             _PRE_CONFIGS.append((name, value))
 
 
diff --git a/alf/data_structures.py b/alf/data_structures.py
index 9cd820990..7f72b6c55 100644
--- a/alf/data_structures.py
+++ b/alf/data_structures.py
@@ -279,7 +279,8 @@ def _generate_time_step(batched,
         if env_id is None:
             env_id = md.arange(batch_size, dtype=md.int32)
         if reward is not None:
-            assert reward.shape[:1] == outer_dims
+            assert reward.shape[:1] == outer_dims, "%s, %s" % (reward.shape,
+                                                               outer_dims)
         if prev_action is not None:
             flat_action = nest.flatten(prev_action)
             assert flat_action[0].shape[:1] == outer_dims
diff --git a/alf/networks/critic_networks.py b/alf/networks/critic_networks.py
index 72a910cc2..6978188a4 100644
--- a/alf/networks/critic_networks.py
+++ b/alf/networks/critic_networks.py
@@ -77,6 +77,7 @@ def __init__(self,
                  joint_fc_layer_params=None,
                  activation=torch.relu_,
                  kernel_initializer=None,
+                 last_bias_init_value=0.0,
                  use_fc_bn=False,
                  use_naive_parallel_network=False,
                  name="CriticNetwork"):
@@ -174,7 +175,8 @@ def __init__(self,
             last_activation=math_ops.identity,
             use_fc_bn=use_fc_bn,
             last_kernel_initializer=last_kernel_initializer,
-            name=name)
+            last_bias_init_value=last_bias_init_value,
+            name=name + ".joint_encoder")
         self._use_naive_parallel_network = use_naive_parallel_network
 
     def make_parallel(self, n):
diff --git a/alf/networks/encoding_networks.py b/alf/networks/encoding_networks.py
index 479401cc0..42329a7b4 100644
--- a/alf/networks/encoding_networks.py
+++ b/alf/networks/encoding_networks.py
@@ -405,6 +405,7 @@ def __init__(self,
                  last_layer_size=None,
                  last_activation=None,
                  last_kernel_initializer=None,
+                 last_bias_init_value=0.0,
                  last_use_fc_bn=False,
                  name="EncodingNetwork"):
         """
@@ -540,7 +541,8 @@ def __init__(self,
                     last_layer_size,
                     activation=last_activation,
                     use_bn=last_use_fc_bn,
-                    kernel_initializer=last_kernel_initializer))
+                    kernel_initializer=last_kernel_initializer,
+                    bias_init_value=last_bias_init_value))
             input_size = last_layer_size
 
         if output_tensor_spec is not None:
diff --git a/alf/trainers/policy_trainer.py b/alf/trainers/policy_trainer.py
index 8a9e078ac..2e9c27dc7 100644
--- a/alf/trainers/policy_trainer.py
+++ b/alf/trainers/policy_trainer.py
@@ -498,6 +498,7 @@ def __init__(self, config: TrainerConfig, ddp_rank: int = -1):
         logging.info(
             "observation_spec=%s" % pprint.pformat(env.observation_spec()))
         logging.info("action_spec=%s" % pprint.pformat(env.action_spec()))
+        logging.info("reward_spec=%s" % pprint.pformat(env.reward_spec()))
 
         # for offline buffer construction
         untransformed_observation_spec = env.observation_spec()
diff --git a/alf/utils/external_configurables.py b/alf/utils/external_configurables.py
index 5a00b7e2e..e9e6cda84 100644
--- a/alf/utils/external_configurables.py
+++ b/alf/utils/external_configurables.py
@@ -46,3 +46,5 @@
 
 gin.external_configurable(torch.nn.init.xavier_normal_,
                           'torch.nn.init.xavier_normal_')
+gin.external_configurable(torch.nn.Embedding, 'torch.nn.Embedding')
+gin.external_configurable(torch.nn.Sequential, 'torch.nn.Sequential')
diff --git a/alf/utils/normalizers.py b/alf/utils/normalizers.py
index 9ef8e2ca0..9f01e7560 100644
--- a/alf/utils/normalizers.py
+++ b/alf/utils/normalizers.py
@@ -138,7 +138,11 @@ def _summary(name, val):
             def _summarize_all(path, t, m2, m):
                 if path:
                     path += "."
-                spec = TensorSpec.from_tensor(m if m2 is None else m2)
+                if m2 is not None:
+                    spec = TensorSpec.from_tensor(m2)
+                else:
+                    assert m is not None
+                    spec = TensorSpec.from_tensor(m)
                 _summary(path + "tensor.batch_min",
                          _reduce_along_batch_dims(t, spec, torch.min))
                 _summary(path + "tensor.batch_max",