diff --git a/aider/utils.py b/aider/utils.py
index c2053e818..c9f41363f 100644
--- a/aider/utils.py
+++ b/aider/utils.py
@@ -12,6 +12,7 @@ def is_image_file(file_name):
     :param file_name: The name of the file to check.
     :return: True if the file is an image, False otherwise.
     """
+    file_name = str(file_name)  # Convert file_name to string
     return any(file_name.endswith(ext) for ext in IMAGE_EXTENSIONS)
 
 
@@ -50,4 +51,6 @@ def is_gpt4_with_openai_base_url(model_name, client):
     :param client: The OpenAI client instance.
     :return: True if conditions are met, False otherwise.
     """
+    if client is None or not hasattr(client, 'base_url'):
+        return False
     return model_name.startswith("gpt-4") and "api.openai.com" in client.base_url.host
diff --git a/tests/test_models.py b/tests/test_models.py
index fe8b681dc..6b2dc58ce 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -29,19 +29,19 @@ class TestModels(unittest.TestCase):
 
     def test_openrouter_model_properties(self):
         client = MagicMock()
-        client.models.list.return_value = {
-            "data": [
-                {
-                    "id": "openai/gpt-4",
-                    "object": "model",
-                    "context_length": "8192",
-                    "pricing": {"prompt": "0.00006", "completion": "0.00012"},
-                }
-            ]
-        }
-        client.models.list.return_value = type(
-            "", (), {"data": client.models.list.return_value["data"]}
-        )()
+        class ModelData:
+            def __init__(self, id, object, context_length, pricing):
+                self.id = id
+                self.object = object
+                self.context_length = context_length
+                self.pricing = pricing
+
+        model_data = ModelData("openai/gpt-4", "model", "8192", {"prompt": "0.00006", "completion": "0.00012"})
+        class ModelList:
+            def __init__(self, data):
+                self.data = data
+
+        client.models.list.return_value = ModelList([model_data])
 
         model = OpenRouterModel(client, "gpt-4")
         self.assertEqual(model.name, "openai/gpt-4")