[Pipelines] Make sure that None functions are correctly not saved (#3080)

src/diffusers/pipelines/pipeline_utils.py

@@ -19,6 +19,7 @@ import importlib
 import inspect
 import os
 import re
+import sys
 import warnings
 from dataclasses import dataclass
 from pathlib import Path
@@ -540,11 +541,9 @@ class DiffusionPipeline(ConfigMixin):
             variant (`str`, *optional*):
                 If specified, weights are saved in the format pytorch_model.<variant>.bin.
         """
-        self.save_config(save_directory)
-
         model_index_dict = dict(self.config)
-        model_index_dict.pop("_class_name")
-        model_index_dict.pop("_diffusers_version")
+        model_index_dict.pop("_class_name", None)
+        model_index_dict.pop("_diffusers_version", None)
         model_index_dict.pop("_module", None)
 
         expected_modules, optional_kwargs = self._get_signature_keys(self)
@@ -557,7 +556,6 @@ class DiffusionPipeline(ConfigMixin):
             return True
 
         model_index_dict = {k: v for k, v in model_index_dict.items() if is_saveable_module(k, v)}
-
         for pipeline_component_name in model_index_dict.keys():
             sub_model = getattr(self, pipeline_component_name)
             model_cls = sub_model.__class__
@@ -571,7 +569,13 @@ class DiffusionPipeline(ConfigMixin):
             save_method_name = None
             # search for the model's base class in LOADABLE_CLASSES
             for library_name, library_classes in LOADABLE_CLASSES.items():
-                library = importlib.import_module(library_name)
+                if library_name in sys.modules:
+                    library = importlib.import_module(library_name)
+                else:
+                    logger.info(
+                        f"{library_name} is not installed. Cannot save {pipeline_component_name} as {library_classes} from {library_name}"
+                    )
+
                 for base_class, save_load_methods in library_classes.items():
                     class_candidate = getattr(library, base_class, None)
                     if class_candidate is not None and issubclass(model_cls, class_candidate):
@@ -581,6 +585,12 @@ class DiffusionPipeline(ConfigMixin):
                 if save_method_name is not None:
                     break
 
+            if save_method_name is None:
+                logger.warn(f"self.{pipeline_component_name}={sub_model} of type {type(sub_model)} cannot be saved.")
+                # make sure that unsaveable components are not tried to be loaded afterward
+                self.register_to_config(**{pipeline_component_name: (None, None)})
+                continue
+
             save_method = getattr(sub_model, save_method_name)
 
             # Call the save method with the argument safe_serialization only if it's supported
@@ -596,6 +606,9 @@ class DiffusionPipeline(ConfigMixin):
 
             save_method(os.path.join(save_directory, pipeline_component_name), **save_kwargs)
 
+        # finally save the config
+        self.save_config(save_directory)
+
     def to(
         self,
         torch_device: Optional[Union[str, torch.device]] = None,