diff --git a/rembg/sessions/base.py b/rembg/sessions/base.py
index 16f988e..8136a03 100644
--- a/rembg/sessions/base.py
+++ b/rembg/sessions/base.py
@@ -28,6 +28,11 @@ class BaseSession:
         else:
             self.providers.extend(_providers)
 
+        model_path = kwargs.get("model_path")
+
+        if model_path is None:
+            raise ValueError("model_path is required")
+
         self.inner_session = ort.InferenceSession(
             str(self.__class__.download_models(*args, **kwargs)),
             providers=self.providers,
diff --git a/rembg/sessions/u2net_custom.py b/rembg/sessions/u2net_custom.py
index 09894b2..7380295 100644
--- a/rembg/sessions/u2net_custom.py
+++ b/rembg/sessions/u2net_custom.py
@@ -34,9 +34,8 @@ class U2netCustomSession(BaseSession):
     @classmethod
     def download_models(cls, *args, **kwargs):
         model_path = kwargs.get("model_path")
-
         if model_path is None:
-            raise ValueError("model_path is required")
+            return
 
         return os.path.abspath(os.path.expanduser(model_path))