validate that the request parameter exists

src/selva/web/application.py

@@ -26,7 +26,7 @@
 )
 from selva.web.converter.error import (
     MissingFromRequestImplError,
-    MissingFromRequestParamImplError,
+    MissingParamConverterImplError,
     MissingRequestParamExtractorImplError,
 )
 from selva.web.converter.from_request import FromRequest
@@ -289,7 +289,7 @@ async def _params_from_request(
                     value = await maybe_async(converter.from_str, param)
                     result[name] = value
                 else:
-                    raise MissingFromRequestParamImplError(param_type)
+                    raise MissingParamConverterImplError(param_type)
             else:
                 if converter := await self._find_param_converter(
                     param_type, FromRequest

src/selva/web/converter/error.py

@@ -11,7 +11,7 @@ def __init__(self, param_type):
         self.param_type = param_type
 
 
-class MissingFromRequestParamImplError(Exception):
+class MissingParamConverterImplError(Exception):
     def __init__(self, param_type):
         super().__init__(
             f"no implementation of '{ParamConverter.__name__}' found for type {param_type}"
@@ -25,3 +25,9 @@ def __init__(self, param_type):
             f"no implementation of '{ParamExtractor.__name__}' found for type {param_type}"
         )
         self.param_type = param_type
+
+
+class PathParamNotFoundError(Exception):
+    def __init__(self, name: str):
+        super().__init__(f"path parameter '{name}' not found")
+        self.name = name

src/selva/web/converter/param_extractor_impl.py

@@ -4,6 +4,7 @@
 from asgikit.requests import Request
 
 from selva.web.converter.decorator import register_param_extractor
+from selva.web.converter.error import PathParamNotFoundError
 
 __all__ = (
     "FromPath",
@@ -37,7 +38,11 @@ def extract(
         else:
             name = metadata.name or parameter_name
 
-        return request["path_params"][name]
+        param = request["path_params"].get(name)
+        if not param:
+            raise PathParamNotFoundError(name)
+
+        return param
 
 
 class FromQuery(FromRequestParam):