diff --git a/datamaxi/aio/cex.py b/datamaxi/aio/cex.py
index e1e949d..90f38db 100644
--- a/datamaxi/aio/cex.py
+++ b/datamaxi/aio/cex.py
@@ -37,8 +37,8 @@ async def __call__(
         symbol: str,
         currency: str = USD,
         interval: Interval = INTERVAL_1D,
-        from_unix: str = None,
-        to_unix: str = None,
+        from_unix: Optional[str] = None,
+        to_unix: Optional[str] = None,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, CandleResponse]:
         """Fetch candle data (async). See ``datamaxi.Datamaxi.cex.candle``."""
@@ -79,7 +79,7 @@ async def exchanges(self, market: Market) -> List[str]:
         return await self.request_endpoint("cex_candle_exchanges", market=market)
 
     async def symbols(
-        self, exchange: str = None, market: Optional[Market] = None
+        self, exchange: Optional[str] = None, market: Optional[Market] = None
     ) -> List[Dict]:
         if market is not None and market not in [SPOT, FUTURES]:
             raise ValueError("market must be either spot or futures")
@@ -97,8 +97,8 @@ async def get(
         exchange: str,
         symbol: str,
         market: Market,
-        currency: str = None,
-        conversion_base: str = None,
+        currency: Optional[str] = None,
+        conversion_base: Optional[str] = None,
         include_source: bool = False,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, TickerResponse]:
@@ -154,8 +154,8 @@ async def symbols(self, exchange: str, market: Market) -> List[str]:
 class AsyncCexFee(AsyncResource):
     async def __call__(
         self,
-        exchange: str = None,
-        symbol: str = None,
+        exchange: Optional[str] = None,
+        symbol: Optional[str] = None,
     ) -> List[Dict]:
         return await self.request_endpoint("cex_fees", exchange=exchange, symbol=symbol)
 
diff --git a/datamaxi/aio/funding_rate.py b/datamaxi/aio/funding_rate.py
index 15b5ed6..4b0e6c1 100644
--- a/datamaxi/aio/funding_rate.py
+++ b/datamaxi/aio/funding_rate.py
@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from typing import Callable, Tuple, List, Union, TYPE_CHECKING
+from typing import Callable, Tuple, List, Union, Optional, TYPE_CHECKING
 
 from datamaxi.aio._core import AsyncResource
 from datamaxi.lib.utils import check_required_parameter, check_required_parameters
@@ -20,8 +20,8 @@ async def history(
         symbol: str,
         page: int = 1,
         limit: int = 1000,
-        fromDateTime: str = None,
-        toDateTime: str = None,
+        fromDateTime: Optional[str] = None,
+        toDateTime: Optional[str] = None,
         sort: SortOrder = DESC,
         pandas: bool = True,
     ) -> Union[Tuple[pd.DataFrame, Callable], Tuple[FundingHistoryResponse, Callable]]:
@@ -75,8 +75,8 @@ async def next_request():
 
     async def latest(
         self,
-        exchange: str = None,
-        symbol: str = None,
+        exchange: Optional[str] = None,
+        symbol: Optional[str] = None,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, LatestFundingRate]:
         res = await self.request_endpoint(
diff --git a/datamaxi/aio/premium.py b/datamaxi/aio/premium.py
index f34c1ff..d412c0c 100644
--- a/datamaxi/aio/premium.py
+++ b/datamaxi/aio/premium.py
@@ -15,27 +15,27 @@
 class AsyncPremium(AsyncResource):
     async def __call__(  # noqa: C901
         self,
-        source_exchange: str = None,
-        target_exchange: str = None,
-        asset: str = None,
-        source_quote: str = None,
-        target_quote: str = None,
+        source_exchange: Optional[str] = None,
+        target_exchange: Optional[str] = None,
+        asset: Optional[str] = None,
+        source_quote: Optional[str] = None,
+        target_quote: Optional[str] = None,
         sort: Optional[SortOrder] = None,
-        key: str = None,
+        key: Optional[str] = None,
         page: int = 1,
         limit: int = 100,
-        currency: str = None,
-        conversion_base: str = None,
-        min_sv: str = None,
-        min_tv: str = None,
+        currency: Optional[str] = None,
+        conversion_base: Optional[str] = None,
+        min_sv: Optional[str] = None,
+        min_tv: Optional[str] = None,
         source_market: Optional[Market] = None,
         target_market: Optional[Market] = None,
         only_transferable: bool = False,
-        network: str = None,
-        premium_type: str = None,
-        token_include: str = None,
-        token_exclude: str = None,
-        query: str = None,
+        network: Optional[str] = None,
+        premium_type: Optional[str] = None,
+        token_include: Optional[str] = None,
+        token_exclude: Optional[str] = None,
+        query: Optional[str] = None,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, PremiumResponse]:
         params = {}
diff --git a/datamaxi/resources/cex_candle.py b/datamaxi/resources/cex_candle.py
index b687a1a..ebb3402 100644
--- a/datamaxi/resources/cex_candle.py
+++ b/datamaxi/resources/cex_candle.py
@@ -34,8 +34,8 @@ def __call__(
         symbol: str,
         currency: str = USD,
         interval: Interval = INTERVAL_1D,
-        from_unix: str = None,
-        to_unix: str = None,
+        from_unix: Optional[str] = None,
+        to_unix: Optional[str] = None,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, CandleResponse]:
         """Fetch candle data
@@ -108,7 +108,7 @@ def exchanges(self, market: Market) -> List[str]:
         return self.request_endpoint("cex_candle_exchanges", market=market)
 
     def symbols(
-        self, exchange: str = None, market: Optional[Market] = None
+        self, exchange: Optional[str] = None, market: Optional[Market] = None
     ) -> List[Dict]:
         """Fetch supported symbols for candle data.
 
diff --git a/datamaxi/resources/cex_fee.py b/datamaxi/resources/cex_fee.py
index cad3c26..e93e251 100644
--- a/datamaxi/resources/cex_fee.py
+++ b/datamaxi/resources/cex_fee.py
@@ -1,4 +1,4 @@
-from typing import Any, List, Dict
+from typing import Any, List, Dict, Optional
 from datamaxi.api import Resource
 from datamaxi.lib.utils import check_required_parameter
 
@@ -17,8 +17,8 @@ def __init__(self, api_key=None, **kwargs: Any):
 
     def __call__(
         self,
-        exchange: str = None,
-        symbol: str = None,
+        exchange: Optional[str] = None,
+        symbol: Optional[str] = None,
     ) -> List[Dict]:
         """Fetch trading fee data
 
diff --git a/datamaxi/resources/cex_ticker.py b/datamaxi/resources/cex_ticker.py
index b9beca7..9b4978e 100644
--- a/datamaxi/resources/cex_ticker.py
+++ b/datamaxi/resources/cex_ticker.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import Any, List, Union, TYPE_CHECKING
+from typing import Any, List, Union, Optional, TYPE_CHECKING
 from datamaxi.api import Resource
 from datamaxi.lib.utils import check_required_parameters
 from datamaxi.resources.responses import TickerResponse
@@ -27,8 +27,8 @@ def get(
         exchange: str,
         symbol: str,
         market: Market,
-        currency: str = None,
-        conversion_base: str = None,
+        currency: Optional[str] = None,
+        conversion_base: Optional[str] = None,
         include_source: bool = False,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, TickerResponse]:
diff --git a/datamaxi/resources/funding_rate.py b/datamaxi/resources/funding_rate.py
index 89c399b..c62a241 100644
--- a/datamaxi/resources/funding_rate.py
+++ b/datamaxi/resources/funding_rate.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import Any, Callable, Tuple, List, Union, TYPE_CHECKING
+from typing import Any, Callable, Tuple, List, Union, Optional, TYPE_CHECKING
 from datamaxi.api import Resource
 from datamaxi.lib.utils import check_required_parameter
 from datamaxi.lib.utils import check_required_parameters
@@ -30,8 +30,8 @@ def history(
         symbol: str,
         page: int = 1,
         limit: int = 1000,
-        fromDateTime: str = None,
-        toDateTime: str = None,
+        fromDateTime: Optional[str] = None,
+        toDateTime: Optional[str] = None,
         sort: SortOrder = DESC,
         pandas: bool = True,
     ) -> Union[Tuple[pd.DataFrame, Callable], Tuple[FundingHistoryResponse, Callable]]:
@@ -107,8 +107,8 @@ def next_request():
 
     def latest(
         self,
-        exchange: str = None,
-        symbol: str = None,
+        exchange: Optional[str] = None,
+        symbol: Optional[str] = None,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, LatestFundingRate]:
         """Fetch latest funding rate data
diff --git a/datamaxi/resources/premium.py b/datamaxi/resources/premium.py
index edcb828..3196c2b 100644
--- a/datamaxi/resources/premium.py
+++ b/datamaxi/resources/premium.py
@@ -26,27 +26,27 @@ def __init__(self, api_key=None, **kwargs: Any):
 
     def __call__(  # noqa: C901
         self,
-        source_exchange: str = None,
-        target_exchange: str = None,
-        asset: str = None,
-        source_quote: str = None,
-        target_quote: str = None,
+        source_exchange: Optional[str] = None,
+        target_exchange: Optional[str] = None,
+        asset: Optional[str] = None,
+        source_quote: Optional[str] = None,
+        target_quote: Optional[str] = None,
         sort: Optional[SortOrder] = None,
-        key: str = None,
+        key: Optional[str] = None,
         page: int = 1,
         limit: int = 100,
-        currency: str = None,
-        conversion_base: str = None,
-        min_sv: str = None,
-        min_tv: str = None,
+        currency: Optional[str] = None,
+        conversion_base: Optional[str] = None,
+        min_sv: Optional[str] = None,
+        min_tv: Optional[str] = None,
         source_market: Optional[Market] = None,
         target_market: Optional[Market] = None,
         only_transferable: bool = False,
-        network: str = None,
-        premium_type: str = None,
-        token_include: str = None,
-        token_exclude: str = None,
-        query: str = None,
+        network: Optional[str] = None,
+        premium_type: Optional[str] = None,
+        token_include: Optional[str] = None,
+        token_exclude: Optional[str] = None,
+        query: Optional[str] = None,
         pandas: bool = True,
     ) -> Union[pd.DataFrame, PremiumResponse]:
         """Fetch premium data