The deprecation warning is shown also if None is explicitly specified

markotoplak · markotoplak · commit f9c4ce3d7b2b · 2023-05-08T14:57:07.000+02:00
diff --git a/sklearn/ensemble/_base.py b/sklearn/ensemble/_base.py
@@ -157,15 +157,18 @@ def _validate_estimator(self, default=None):
 
         if self.estimator is not None:
             self.estimator_ = self.estimator
-        elif self.base_estimator not in [None, "deprecated"]:
+        elif self.base_estimator != "deprecated":
             warnings.warn(
                 (
                     "`base_estimator` was renamed to `estimator` in version 1.2 and "
                     "will be removed in 1.4."
                 ),
                 FutureWarning,
             )
-            self.estimator_ = self.base_estimator
+            if self.base_estimator is not None:
+                self.estimator_ = self.base_estimator
+            else:
+                self.estimator_ = default
         else:
             self.estimator_ = default
 
