Allow Success() result with no params (#172)

Author: bcb

jsonrpcserver/result.py

@@ -23,7 +23,7 @@ def my_method(request: Request) -> Result:
 
     return Error(-32602, "Color is invalid")
 """
-from typing import Any, NamedTuple, Union
+from typing import Any, NamedTuple, Optional, Union
 
 from . import status
 
@@ -33,7 +33,7 @@ def my_method(request: Request) -> Result:
 
 
 class Success(NamedTuple):
-    result: str
+    result: Optional[str] = None
 
 
 class Error(NamedTuple):