refactor: Update type annotations

2 files changed, 15 insertions, 1 deletions

diff --git a/sphinx/pycode/ast.py b/sphinx/pycode/ast.py
index 9664e7edb..3f4717f45 100644
--- a/sphinx/pycode/ast.py
+++ b/sphinx/pycode/ast.py
@@ -10,6 +10,7 @@
 
 import sys
 from typing import Dict, List, Type, Optional
+from typing import overload
 
 if sys.version_info > (3, 8):
     import ast
@@ -58,6 +59,16 @@ def parse(code: str, mode: str = 'exec') -> "ast.AST":
         return ast.parse(code, mode=mode)
 
 
+@overload
+def unparse(node: None) -> None:
+    ...
+
+
+@overload
+def unparse(node: ast.AST) -> str:
+    ...
+
+
 def unparse(node: Optional[ast.AST]) -> Optional[str]:
     """Unparse an AST to string."""
     if node is None:
diff --git a/sphinx/pycode/parser.py b/sphinx/pycode/parser.py
index a77654939..7eb2419c0 100644
--- a/sphinx/pycode/parser.py
+++ b/sphinx/pycode/parser.py
@@ -93,7 +93,10 @@ def dedent_docstring(s: str) -> str:
 
     dummy.__doc__ = s
     docstring = inspect.getdoc(dummy)
-    return docstring.lstrip("\r\n").rstrip("\r\n")
+    if docstring:
+        return docstring.lstrip("\r\n").rstrip("\r\n")
+    else:
+        return ""
 
 
 class Token: