check if autodoc_defaults are str, fix tests

1 files changed, 3 insertions, 3 deletions

diff --git a/sphinx/ext/autodoc/directive.py b/sphinx/ext/autodoc/directive.py
index 47c6766e5..c88600ff2 100644
--- a/sphinx/ext/autodoc/directive.py
+++ b/sphinx/ext/autodoc/directive.py
@@ -87,7 +87,7 @@ def process_documenter_options(documenter: "Type[Documenter]", config: Config, o
         else:
             negated = options.pop('no-' + name, True) is None
             if name in config.autodoc_default_options and not negated:
-                if name in options:
+                if name in options and isinstance(config.autodoc_default_options[name], str):
                     # take value from options if present or extend it
                     # with autodoc_default_options if necessary
                     if name in AUTODOC_EXTENDABLE_OPTIONS:
@@ -97,9 +97,9 @@ def process_documenter_options(documenter: "Type[Documenter]", config: Config, o
                 else:
                     options[name] = config.autodoc_default_options[name]
 
-            elif isinstance(options.get(name), str) and options[name].startswith('+'):
+            elif options.get(name) is not None:
                 # remove '+' from option argument if there's nothing to merge it with
-                options[name] = options[name].strip('+')
+                options[name] = options[name].lstrip('+')
 
     return Options(assemble_option_dict(options.items(), documenter.option_spec))