diff --git a/mammoth/trainer.py b/mammoth/trainer.py
index c1e447a5..8dfd4efc 100644
--- a/mammoth/trainer.py
+++ b/mammoth/trainer.py
@@ -311,7 +311,8 @@ def train(
             if device_context.is_master():
                 sampled_task_counts = self.task_queue_manager.sampled_task_counts
             else:
-                sampled_task_counts = None
+                from collections import Counter
+                sampled_task_counts =  Counter()
             report_stats = self._maybe_report_training(
                 step,
                 train_steps,
diff --git a/mammoth/utils/report_manager.py b/mammoth/utils/report_manager.py
index 9a7d4a91..08911124 100644
--- a/mammoth/utils/report_manager.py
+++ b/mammoth/utils/report_manager.py
@@ -59,7 +59,7 @@ def report_training(
         patience,
         report_stats,
         multigpu=False,
-        sampled_task_counts=None,
+        sampled_task_counts={},
         optimizer=None,
     ):
         """
diff --git a/mammoth/utils/statistics.py b/mammoth/utils/statistics.py
index 0c680360..e5d8ce6c 100644
--- a/mammoth/utils/statistics.py
+++ b/mammoth/utils/statistics.py
@@ -34,7 +34,7 @@ def __init__(self, loss=0, n_words=0, n_correct=None):
         self.magnitude_denom = 0
         self.param_magnitudes = Counter()
         self.grad_magnitudes = Counter()
-
+        
     @classmethod
     def from_loss_logits_target(cls, loss: float, logits, target, padding_idx):
         """