Allow None for jitter kwarg (typing)

Author: bgreen-litl

backoff/_decorator.py

@@ -29,7 +29,7 @@ def on_predicate(wait_gen: _WaitGenerator,
                  *,
                  max_tries: Optional[_MaybeCallable[int]] = None,
                  max_time: Optional[_MaybeCallable[float]] = None,
-                 jitter: _Jitterer = full_jitter,
+                 jitter: Union[_Jitterer, None] = full_jitter,
                  on_success: Union[_Handler, Iterable[_Handler]] = None,
                  on_backoff: Union[_Handler, Iterable[_Handler]] = None,
                  on_giveup: Union[_Handler, Iterable[_Handler]] = None,
@@ -125,7 +125,7 @@ def on_exception(wait_gen: _WaitGenerator,
                  *,
                  max_tries: Optional[_MaybeCallable[int]] = None,
                  max_time: Optional[_MaybeCallable[float]] = None,
-                 jitter: _Jitterer = full_jitter,
+                 jitter: Union[_Jitterer, None] = full_jitter,
                  giveup: _Predicate[Exception] = lambda e: False,
                  on_success: Union[_Handler, Iterable[_Handler]] = None,
                  on_backoff: Union[_Handler, Iterable[_Handler]] = None,