diff --git a/django/contrib/admin/__init__.py b/django/contrib/admin/__init__.py
index bc2fa3eb51e4..9fd1825921d9 100644
--- a/django/contrib/admin/__init__.py
+++ b/django/contrib/admin/__init__.py
@@ -14,6 +14,7 @@
 from django.contrib.admin.options import (
     HORIZONTAL,
     VERTICAL,
+    Action,
     ActionLocation,
     ModelAdmin,
     ShowFacets,
@@ -25,6 +26,7 @@
 
 __all__ = [
     "action",
+    "Action",
     "ActionLocation",
     "display",
     "register",
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 7ac02f8a50a0..c88a10118a6e 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -710,7 +710,7 @@ def _set_pk_val(self, value):
     def _is_pk_set(self, meta=None):
         pk_val = self._get_pk_val(meta)
 
-        def _is_set(value):
+        def _is_unset(value):
             return (
                 value is None
                 # Empty value when db_default is used.
@@ -718,8 +718,8 @@ def _is_set(value):
             )
 
         return not (
-            _is_set(pk_val)
-            or (isinstance(pk_val, tuple) and any(_is_set(f) for f in pk_val))
+            _is_unset(pk_val)
+            or (isinstance(pk_val, tuple) and any(_is_unset(f) for f in pk_val))
         )
 
     def get_deferred_fields(self):