♿ allow extra param with default value

nonebot/params.py

@@ -1,6 +1,8 @@
 import inspect
 from typing import Any, Dict, Optional
 
+from pydantic.fields import Undefined
+
 from nonebot.typing import T_State
 from nonebot.dependencies import Param
 from nonebot.adapters import Bot, Event
@@ -69,4 +71,14 @@ class ExceptionParam(Param):
         return exception
 
 
+class DefaultParam(Param):
+
+    @classmethod
+    def _check(cls, name: str, param: inspect.Parameter) -> bool:
+        return param.default != param.empty
+
+    def _solve(self, **kwargs: Any) -> Any:
+        return Undefined
+
+
 from nonebot.matcher import Matcher