refactor: Change load_external_modules default value to None to s…

…upport new default mode in Griffe

docs/usage/index.md

@@ -141,8 +141,11 @@ More details at [Finding modules](#finding-modules).
 This option allows resolving aliases (imports) to any external module.
 Modules are considered external when they are not part
 of the package your are injecting documentation for.
-Enabling this option will tell the handler to resolve aliases recursively
+Setting this option to `True` will tell the handler to resolve aliases recursively
 when they are made public through the [`__all__`][__all__] variable.
+By default, the handler will only resolve aliases when they point at a private sibling
+of the source package, for example aliases going from `ast` to `_ast`.
+Set `load_external_modules` to `False` to prevent even that.
 
 WARNING: **Use with caution**
 This can load a *lot* of modules through [Griffe],

src/mkdocstrings_handlers/python/handler.py

@@ -197,7 +197,7 @@ def __init__(
         config_file_path: str | None = None,
         paths: list[str] | None = None,
         locale: str = "en",
-        load_external_modules: bool = False,
+        load_external_modules: bool | None = None,
         **kwargs: Any,
     ) -> None:
         """Initialize the handler.
@@ -474,7 +474,7 @@ def get_handler(
     config_file_path: str | None = None,
     paths: list[str] | None = None,
     locale: str = "en",
-    load_external_modules: bool = False,
+    load_external_modules: bool | None = None,
     **config: Any,  # noqa: ARG001
 ) -> PythonHandler:
     """Simply return an instance of `PythonHandler`.