diff --git a/package.json b/package.json
index d62b56a..4f6f08b 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "imdux",
-    "version": "0.1.5",
+    "version": "0.1.6",
     "description": "A redux helper for react & hooks & typescript developers.",
     "main": "dist/imdux.js",
     "types": "src/types.d.ts",
diff --git a/src/test/imdux.test.ts b/src/test/imdux.test.ts
index 531e10b..5ee418b 100644
--- a/src/test/imdux.test.ts
+++ b/src/test/imdux.test.ts
@@ -31,6 +31,9 @@ describe("imdux object state", () => {
         array(draft: State, payload: Array<number>) {
             draft.array = payload;
         },
+        optional(draft: State, payload?: number) {
+            draft.count -= 1;
+        },
     };
 
     const reducers2 = {
@@ -144,6 +147,8 @@ describe("imdux object state", () => {
         Dispatch.home.hide("3");
         Dispatch.home.hide(null);
         (a: "1" | "2" | null) => Dispatch.home.hide(a);
+        Dispatch.home.optional(1);
+        Dispatch.home.optional(undefined);
     });
 });
 
diff --git a/src/types.d.ts b/src/types.d.ts
index b5d569f..86d3343 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -17,8 +17,10 @@ export namespace Imdux {
         redux: Redux.Store<any, Redux.AnyAction>;
     }
 
+    export type InferActionDispathFunction<T> = T extends (...arg: infer A) => any ? A extends [any] ? () => void : T extends (draft: any, payload: infer R) => any ? (payload: R) => void : never : never;
+
     export type InferActionDispath<T> = {
-        [K in keyof T]: T[K] extends (draft: any) => any ? () => void : T[K] extends (draft: any, payload: infer R) => any ? (payload: R) => void : unknown
+        [K in keyof T]: InferActionDispathFunction<T[K]>
     }
 
     export type InferDispatch<T> = {