fix: return a non null list

hermetic_build/common/model/config_change.py

@@ -62,7 +62,7 @@ def __init__(self, commit: Commit, libraries: set[str]):
 
 
 class ConfigChange:
-    ALL_LIBRARIES_CHANGED = None
+    ALL_LIBRARIES_CHANGED = "ALL_LIBRARIES"
 
     def __init__(
         self,
@@ -74,16 +74,17 @@ def __init__(
         self.baseline_config = baseline_config
         self.current_config = current_config
 
-    def get_changed_libraries(self) -> Optional[list[str]]:
+    def get_changed_libraries(self) -> list[str]:
         """
         Returns a unique, sorted list of library name of changed libraries.
-        None if there is a repository level change, which means all libraries
-        in the current_config will be generated.
+        A special list [ALL_LIBRARIES], will be returned if there is a
+        repository level change, which means all libraries in the current_config
+        will be generated.
 
         :return: library names of change libraries.
         """
         if ChangeType.REPO_LEVEL_CHANGE in self.change_to_libraries:
-            return ConfigChange.ALL_LIBRARIES_CHANGED
+            return [ConfigChange.ALL_LIBRARIES_CHANGED]
         library_names = set()
         for change_type, library_changes in self.change_to_libraries.items():
             if change_type == ChangeType.GOOGLEAPIS_COMMIT:

hermetic_build/library_generation/cli/entry_point.py

@@ -44,6 +44,7 @@ def main(ctx):
     show_default=True,
     help="""
     A list of library names that will be generated, separated by comma.
+    If set to `ALL_LIBRARIES`, all libraries will be generated.
     The library name of a library is the value of library_name or api_shortname,
     if library_name is not specified, in the generation configuration.
     """,
@@ -157,7 +158,11 @@ def _needs_full_repo_generation(generation_config: GenerationConfig) -> bool:
 def _parse_library_name_from(
     includes: Optional[str], generation_config: GenerationConfig
 ) -> Optional[list[str]]:
-    if includes is None or _needs_full_repo_generation(generation_config):
+    if (
+        includes is None
+        or includes == "ALL_LIBRARIES"
+        or _needs_full_repo_generation(generation_config)
+    ):
         return None
     return [library_name.strip() for library_name in includes.split(",")]