diff --git a/sinch/core/exceptions.py b/sinch/core/exceptions.py
index 76b44b0..d1de78b 100644
--- a/sinch/core/exceptions.py
+++ b/sinch/core/exceptions.py
@@ -1,8 +1,9 @@
+from typing import Union
 from sinch.core.models.http_response import HTTPResponse
 
 
 class SinchException(Exception):
-    def __init__(self, message: str, response: HTTPResponse, is_from_server: bool):
+    def __init__(self, message: str, response: Union[HTTPResponse, None], is_from_server: bool):
         self.is_from_server = is_from_server
         self.response_status_code = response.status_code if response else None
         self.http_response = response
diff --git a/sinch/core/token_manager.py b/sinch/core/token_manager.py
index 3766749..c5bd529 100644
--- a/sinch/core/token_manager.py
+++ b/sinch/core/token_manager.py
@@ -1,12 +1,15 @@
 from enum import Enum
 from abc import ABC, abstractmethod
-from typing import Optional
+from typing import Optional, TYPE_CHECKING
 
 from sinch.domains.authentication.models.authentication import OAuthToken
 from sinch.domains.authentication.endpoints.oauth import OAuthEndpoint
 from sinch.core.exceptions import ValidationException
 from sinch.core.models.http_response import HTTPResponse
 
+if TYPE_CHECKING:
+    from sinch.core.clients.sinch_client_base import ClientBase
+
 
 class TokenState(Enum):
     VALID = "VALID"
@@ -15,7 +18,7 @@ class TokenState(Enum):
 
 
 class TokenManagerBase(ABC):
-    def __init__(self, sinch):
+    def __init__(self, sinch: 'ClientBase') -> None:
         self.sinch = sinch
         self.token: Optional[OAuthToken] = None
         self.token_state = TokenState.INVALID
@@ -24,11 +27,11 @@ def __init__(self, sinch):
     def get_auth_token(self) -> Optional[OAuthToken]:
         pass
 
-    def invalidate_expired_token(self):
+    def invalidate_expired_token(self) -> None:
         self.token = None
         self.token_state = TokenState.EXPIRED
 
-    def handle_invalid_token(self, http_response: HTTPResponse):
+    def handle_invalid_token(self, http_response: HTTPResponse) -> None:
         if http_response.headers.get("www-authenticate") and "expired" in http_response.headers["www-authenticate"]:
             self.invalidate_expired_token()