diff --git a/pyproject.toml b/pyproject.toml
index 0a4209fe..518a86e8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -124,7 +124,9 @@ extra_checks = true
 enable_error_code = [
     "exhaustive-match",
     "ignore-without-code",
+    "mutable-override",
     "redundant-expr",
+    "truthy-bool",
     "truthy-iterable",
     "unused-awaitable",
 ]
diff --git a/tenacity/__init__.py b/tenacity/__init__.py
index 21d7f507..e993396c 100644
--- a/tenacity/__init__.py
+++ b/tenacity/__init__.py
@@ -88,6 +88,11 @@
 except ImportError:
     tornado = None  # type: ignore[assignment]
 
+# mypy resolves `tornado` to the module (it only ever sees the `try` branch),
+# so testing the module object for truthiness reads as an always-true check.
+# Keep the availability answer in a plain bool instead.
+_HAS_TORNADO = tornado is not None
+
 if t.TYPE_CHECKING:
     if sys.version_info >= (3, 11):
         from typing import Self
@@ -148,8 +153,8 @@ class BaseAction:
     - NAME: for identification in retry object methods and callbacks
     """
 
-    REPR_FIELDS: t.Sequence[str] = ()
-    NAME: str | None = None
+    REPR_FIELDS: t.ClassVar[t.Sequence[str]] = ()
+    NAME: t.ClassVar[str | None] = None
 
     def __repr__(self) -> str:
         state_str = ", ".join(
@@ -162,8 +167,8 @@ def __str__(self) -> str:
 
 
 class RetryAction(BaseAction):
-    REPR_FIELDS = ("sleep",)
-    NAME = "retry"
+    REPR_FIELDS: t.ClassVar[t.Sequence[str]] = ("sleep",)
+    NAME: t.ClassVar[str | None] = "retry"
 
     def __init__(self, sleep: t.SupportsFloat) -> None:
         self.sleep = float(sleep)
@@ -403,12 +408,7 @@ def _run_retry(self, retry_state: "RetryCallState") -> None:
         self.iter_state.retry_run_result = self.retry(retry_state)
 
     def _run_wait(self, retry_state: "RetryCallState") -> None:
-        if self.wait:
-            sleep = self.wait(retry_state)
-        else:
-            sleep = 0.0
-
-        retry_state.upcoming_sleep = sleep
+        retry_state.upcoming_sleep = self.wait(retry_state)
 
     def _run_stop(self, retry_state: "RetryCallState") -> None:
         self.statistics["delay_since_first_attempt"] = retry_state.seconds_since_start
@@ -770,7 +770,7 @@ def wrap(f: t.Callable[P, R]) -> _RetryDecorated[P, R]:
         ):
             r = AsyncRetrying(*dargs, **dkw)
         elif (
-            tornado
+            _HAS_TORNADO
             and hasattr(tornado.gen, "is_coroutine_function")
             and tornado.gen.is_coroutine_function(f)
         ):
@@ -785,7 +785,7 @@ def wrap(f: t.Callable[P, R]) -> _RetryDecorated[P, R]:
 
 from tenacity.asyncio import AsyncRetrying  # noqa: E402
 
-if tornado:
+if _HAS_TORNADO:
     from tenacity.tornadoweb import TornadoRetrying
 
 
diff --git a/tenacity/asyncio/__init__.py b/tenacity/asyncio/__init__.py
index 6291b02f..a91ca577 100644
--- a/tenacity/asyncio/__init__.py
+++ b/tenacity/asyncio/__init__.py
@@ -142,12 +142,9 @@ async def _run_retry(self, retry_state: "RetryCallState") -> None:  # type: igno
         )
 
     async def _run_wait(self, retry_state: "RetryCallState") -> None:  # type: ignore[override]
-        if self.wait:
-            sleep = await _utils.wrap_to_async_func(self.wait)(retry_state)
-        else:
-            sleep = 0.0
-
-        retry_state.upcoming_sleep = sleep
+        retry_state.upcoming_sleep = await _utils.wrap_to_async_func(self.wait)(
+            retry_state
+        )
 
     async def _run_stop(self, retry_state: "RetryCallState") -> None:  # type: ignore[override]
         self.statistics["delay_since_first_attempt"] = retry_state.seconds_since_start