diff --git a/none/command.py b/none/command.py
index 2c36ee87..4681321f 100644
--- a/none/command.py
+++ b/none/command.py
@@ -247,7 +247,8 @@ class CommandSession(BaseSession):
     @property
     def is_valid(self) -> bool:
         """Check if the session is expired or not."""
-        if self._last_interaction and \
+        if self.bot.config.SESSION_EXPIRE_TIMEOUT and \
+                self._last_interaction and \
                 datetime.now() - self._last_interaction > \
                 self.bot.config.SESSION_EXPIRE_TIMEOUT:
             return False
diff --git a/none/default_config.py b/none/default_config.py
index 575667aa..2549c399 100644
--- a/none/default_config.py
+++ b/none/default_config.py
@@ -15,21 +15,25 @@ For example:
 """
 
 from datetime import timedelta
+from typing import Container, Union, Iterable, Pattern, Optional
 
-API_ROOT = ''
-SECRET = ''
-ACCESS_TOKEN = ''
-HOST = '127.0.0.1'
-PORT = 8080
-DEBUG = True
+from .expression import Expression_T
 
-SUPERUSERS = set()
-NICKNAME = ''
-COMMAND_START = {'/', '!', '／', '！'}
-COMMAND_SEP = {'/', '.'}
-SESSION_EXPIRE_TIMEOUT = timedelta(minutes=5)
-SESSION_RUNNING_EXPRESSION = '您有命令正在执行，请稍后再试'
-SHORT_MESSAGE_MAX_LENGTH = 50
+API_ROOT: str = ''
+SECRET: str = ''
+ACCESS_TOKEN: str = ''
+HOST: str = '127.0.0.1'
+PORT: int = 8080
+DEBUG: bool = True
+
+SUPERUSERS: Container[int] = set()
+NICKNAME: Union[str, Iterable[str]] = ''
+COMMAND_START: Iterable[Union[str, Pattern]] = {'/', '!', '／', '！'}
+COMMAND_SEP: Iterable[Union[str, Pattern]] = {'/', '.'}
+SESSION_EXPIRE_TIMEOUT: Optional[timedelta] = timedelta(minutes=5)
+SESSION_RUN_TIMEOUT: Optional[timedelta] = None
+SESSION_RUNNING_EXPRESSION: Expression_T = '您有命令正在执行，请稍后再试'
+SHORT_MESSAGE_MAX_LENGTH: int = 50
 
 APSCHEDULER_CONFIG = {
     'apscheduler.timezone': 'Asia/Shanghai'
diff --git a/none/expression.py b/none/expression.py
index 85ea46b9..037a41eb 100644
--- a/none/expression.py
+++ b/none/expression.py
@@ -3,8 +3,10 @@ from typing import Union, Sequence, Callable
 
 from aiocqhttp import message
 
+Expression_T = Union[str, Sequence[str], Callable]
 
-def render(expr: Union[str, Sequence[str], Callable], *, escape_args=True,
+
+def render(expr: Expression_T, *, escape_args=True,
            **kwargs) -> str:
     """
     Render an expression to message string.
diff --git a/none/natural_language.py b/none/natural_language.py
index 4a7caf6a..b5f768ae 100644
--- a/none/natural_language.py
+++ b/none/natural_language.py
@@ -86,11 +86,10 @@ async def handle_natural_language(bot: NoneBot, ctx: Dict[str, Any]) -> bool:
     msg = str(ctx['message'])
     if bot.config.NICKNAME:
         # check if the user is calling me with my nickname
-        if not isinstance(bot.config.NICKNAME, Iterable):
-            # noinspection PyUnusedLocal
+        if isinstance(bot.config.NICKNAME, str) or \
+                not isinstance(bot.config.NICKNAME, Iterable):
             nicknames = (bot.config.NICKNAME,)
         else:
-            # noinspection PyUnusedLocal
             nicknames = filter(lambda n: n, bot.config.NICKNAME)
         m = re.search(rf'^({"|".join(nicknames)})[\s,，]+', msg, re.IGNORECASE)
         if m: