WIP: fix JsonRpcRequest to be valid json

fix/types: JsonRpcParams should be valid JSON values

`undefined` is not valid JSON.

https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf
(Section 5):

    A JSON value can be an object, array, number, string, true, false, or null.

fix/json: coerce away `undefined` params in JsonRpcParamsStruct

src/json.ts

@@ -180,14 +180,28 @@ export type JsonRpcError = OptionalField<
 export const JsonRpcParamsStruct = optional(
   union([record(string(), JsonStruct), array(JsonStruct)]),
 );
+
 export type JsonRpcParams = Infer<typeof JsonRpcParamsStruct>;
 
-export const JsonRpcRequestStruct = object({
+export const JsonRpcRequestStruct: Struct<
+  {
+    id: number | null | string;
+    method: string;
+    jsonrpc: '2.0';
+    params?: Json[] | Record<string, Json>;
+  },
+  {
+    id: Struct<string | number | null, null>;
+    jsonrpc: Struct<'2.0', '2.0'>;
+    method: Struct<string, null>;
+    params?: any;
+  }
+> = object({
   id: JsonRpcIdStruct,
   jsonrpc: JsonRpcVersionStruct,
   method: string(),
   params: JsonRpcParamsStruct,
-});
+}) as any;
 
 export type InferWithParams<
   Type extends Struct<any>,