Merge pull request #291 from pobonomo/1.4.x

Deal with empty list of column in column transformer

src/gurobi_ml/sklearn/column_transformer.py

@@ -65,6 +65,9 @@ def _mip_model(self, **kwargs):
         transformers = {k.lower(): v for k, v in sklearn_transformers().items()}
         transformed = []
         for name, trans, cols in column_transform.transformers_:
+            if len(cols) == 0:
+                # If there are no columns to transform nothing to do
+                continue
             if trans == "passthrough":
                 if isinstance(cols, str) or isinstance(cols[0], str):
                     transformed.append(_input.loc[:, cols])