From 4659fc21a92c3ff8c7019b56bf2e519bb5583ce5 Mon Sep 17 00:00:00 2001
From: picnixz <10796600+picnixz@users.noreply.github.com>
Date: Fri, 7 Apr 2023 01:28:48 +0200
Subject: [PATCH] Fix translator class check in ``SigElementFallbackTransform``
 (#11283)

---
 sphinx/transforms/post_transforms/__init__.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sphinx/transforms/post_transforms/__init__.py b/sphinx/transforms/post_transforms/__init__.py
index 1801d2c0949..4a963d31b87 100644
--- a/sphinx/transforms/post_transforms/__init__.py
+++ b/sphinx/transforms/post_transforms/__init__.py
@@ -237,7 +237,11 @@ def has_visitor(translator: type[nodes.NodeVisitor], node: type[Element]) -> boo
             return hasattr(translator, "visit_%s" % node.__name__)
 
         translator = self.app.builder.get_translator_class()
-        if isinstance(translator, SphinxTranslator):
+        if translator is None:
+            # do nothing if no translator class is specified (e.g., on a dummy builder)
+            return
+
+        if issubclass(translator, SphinxTranslator):
             # subclass of SphinxTranslator supports desc_sig_element nodes automatically.
             return