diff --git a/notebooks/Jungfrau/Jungfrau_Gain_Correct_and_Verify_NBC.ipynb b/notebooks/Jungfrau/Jungfrau_Gain_Correct_and_Verify_NBC.ipynb
index 3cff265cbb2f1314c335a23ffdad9144d947b3c8..a5f9a894ab464fb0a81b32662591578d23e299b0 100644
--- a/notebooks/Jungfrau/Jungfrau_Gain_Correct_and_Verify_NBC.ipynb
+++ b/notebooks/Jungfrau/Jungfrau_Gain_Correct_and_Verify_NBC.ipynb
@@ -76,6 +76,7 @@
     "import sys\n",
     "import warnings\n",
     "from functools import partial\n",
+    "from logging import warn\n",
     "from pathlib import Path\n",
     "\n",
     "import h5py\n",
@@ -481,6 +482,7 @@
    "outputs": [],
    "source": [
     "# Loop over modules\n",
+    "empty_seq = 0\n",
     "for local_karabo_da, mapped_files_module in mapped_files.items():\n",
     "    instrument_src_kda = instrument_src.format(int(local_karabo_da[-2:]))\n",
     "\n",
@@ -502,8 +504,9 @@
     "        # Raise a WARNING if this sequence has no trains to correct.\n",
     "        # Otherwise, print number of trains with no data.\n",
     "        if corr_ntrains == 0:\n",
-    "            print(f\"\\t- WARNING: No trains to correct for {sequence_file.name}: \"\n",
-    "                  f\"Skipping the processing of this file.\")\n",
+    "            warn(f\"No trains to correct for {sequence_file.name}: \"\n",
+    "                 \"Skipping the processing of this file.\")\n",
+    "            empty_seq += 1\n",
     "            continue\n",
     "        elif len(all_train_ids) != corr_ntrains:\n",
     "            print(f\"{sequence_file.name} has {len(seq_dc_adc.train_ids) - corr_ntrains} \"\n",
@@ -601,7 +604,9 @@
     "            # Create METDATA datasets\n",
     "            outp_file.create_metadata(like=seq_dc)\n",
     "\n",
-    "        step_timer.done_step(f'Saving data time.')"
+    "        step_timer.done_step(f'Saving data time.')\n",
+    "if empty_seq == sum([len(i) for i in mapped_files.values()]):\n",
+    "    raise ValueError(\"No valid trains for RAW data to correct.\")"
    ]
   },
   {
diff --git a/src/cal_tools/step_timing.py b/src/cal_tools/step_timing.py
index 790021f0568f5e20d6111904f01c15847cb8fe0b..e95362444b7b315c758d32eb8b2bb8621b3c56ab 100644
--- a/src/cal_tools/step_timing.py
+++ b/src/cal_tools/step_timing.py
@@ -27,7 +27,8 @@ class StepTimer:
 
     def timespan(self):
         """Wall time from 1st call to start() to last start() or done_step()"""
-        return self.t_latest - self.t0
+        if self.t_latest is not None and self.t0 is not None:
+            return self.t_latest - self.t0
 
     def print_summary(self):
         """Show mean & std for each step"""