Fix error when py_object has custom __eq__

PiperOrigin-RevId: 414969859

Author: tensorflower-gardener

tools/tensorflow_docs/api_generator/doc_generator_visitor.py

@@ -45,7 +45,7 @@ def maybe_singleton(py_object: Any) -> bool:
   is_immutable_type = isinstance(py_object, immutable_types)
 
   # Check if the object is the empty tuple.
-  return is_immutable_type or py_object == ()
+  return is_immutable_type or (isinstance(py_object, tuple) and py_object == ())  # pylint: disable=g-explicit-bool-comparison
 
 
 class ApiTreeNode(object):