Fix device map nits

src/diffusers/pipelines/pipeline_loading_utils.py

@@ -568,15 +568,17 @@ def _get_final_device_map(device_map, pipeline_class, passed_class_obj, init_dic
 
     # Obtain a dictionary mapping the model-level components to the available
     # devices based on the maximum memory and the model sizes.
-    device_id_component_mapping = _assign_components_to_devices(
-        module_sizes, max_memory, device_mapping_strategy=device_map
-    )
+    final_device_map = None
+    if len(max_memory) > 0:
+        device_id_component_mapping = _assign_components_to_devices(
+            module_sizes, max_memory, device_mapping_strategy=device_map
+        )
 
-    # Obtain the final device map, e.g., `{"unet": 0, "text_encoder": 1, "vae": 1, ...}`
-    final_device_map = {}
-    for device_id, components in device_id_component_mapping.items():
-        for component in components:
-            final_device_map[component] = device_id
+        # Obtain the final device map, e.g., `{"unet": 0, "text_encoder": 1, "vae": 1, ...}`
+        final_device_map = {}
+        for device_id, components in device_id_component_mapping.items():
+            for component in components:
+                final_device_map[component] = device_id
 
     return final_device_map