added null input parameter type

src/structures/Parameter.ts

@@ -153,3 +153,9 @@ export class ObjectID {
         }
     }
 }
+
+export class NullParameter extends InputParameter {
+    constructor(parameter: Parameter) {
+        super(parameter, null);
+    }
+}

src/types/Parameter.ts

@@ -2,7 +2,7 @@ import { ObjectID } from "../structures/Parameter.js";
 
 export type ParameterType = "string" | "boolean" | "number" | "user" | "role" | "channel" | "mentionable";
 
-export type ParameterResolvable = string | boolean | number | ObjectID | undefined;
+export type ParameterResolvable = string | boolean | number | ObjectID | null | undefined; //remove "undefined"
 
 /**
  * @interface