fixes

clinica/iotools/utils/pipeline_handling.py

@@ -91,9 +91,17 @@ def _extract_metrics_from_pipeline(
         pvc_restriction,
         tracers_selection,
     )
-    pipeline_df = pd.DataFrame.from_records(
-        records, index=["participant_id", "session_id"]
-    )
+    if records:
+        pipeline_df = pd.DataFrame.from_records(
+            records, index=["participant_id", "session_id"]
+        )
+    else:
+        pipeline_df = pd.DataFrame.from_records(
+            records, columns=["participant_id", "session_id"]
+        )
+        pipeline_df.set_index(
+            ["participant_id", "session_id"], inplace=True, verify_integrity=True
+        )
     summary_df = _generate_summary(
         pipeline_df, pipeline, ignore_groups=group_selection == [""]
     )

test/unittests/iotools/utils/test_data_handling.py

@@ -483,7 +483,7 @@ def test_add_data_to_merge_file_from_caps_empty_pipeline(tmp_path):
             ],
         }
     )
-
+    (tmp_path / "groups").mkdir()
     with pytest.raises(
         FileNotFoundError,
         match=(

test/unittests/iotools/utils/test_pipeline_handling.py

@@ -271,14 +271,14 @@ def test_extract_metrics_from_pipeline_errors(tmp_path):
 def test_extract_metrics_from_pipeline(tmp_path):
     from clinica.iotools.utils.pipeline_handling import _extract_metrics_from_pipeline
 
+    (tmp_path / "groups").mkdir()
     df = pd.DataFrame([["bar", "bar"]], columns=["participant_id", "session_id"])
     assert _extract_metrics_from_pipeline(
         tmp_path, df, ["metrics"], PipelineNameForMetricExtraction.T1_VOLUME
     ) == (
         df,
         None,
     )
-    (tmp_path / "groups").mkdir()
     (tmp_path / "groups" / "UnitTest").mkdir()
     x, y = _extract_metrics_from_pipeline(
         tmp_path, df, ["metrics"], PipelineNameForMetricExtraction.T1_VOLUME