Update type and doc for removing values from config

Author: JustWalters

README.md

@@ -183,6 +183,8 @@ const { sub: visitorId } = await jwt.decode(token);
  */
 res.send({ foo: 'bar' }); // will save foo in the installation config.
 // or
+res.send({ foo: null }); // will remove foo from the installation config.
+// or
 res.sendFailed('This step has failed validation.'); // prevent the installer from progressing.
 
 /**

src/sdk/handlers.ts

@@ -24,6 +24,10 @@ import EnvoyResponse, {
 
 type SomeObject = Record<string, unknown>;
 
+type Nullable<T> = {
+  [P in keyof T]: T[P] | null;
+};
+
 type Result = Promise<void> | void;
 
 /**
@@ -94,7 +98,7 @@ export type SelectedValuesRouteHandler<Config = SomeObject, Additions = SomeObje
  * @category Handler
  */
 export type ValidationRouteHandler<Config = SomeObject, Payload = SomeObject, Additions = SomeObject> =
-  (req: EnvoyValidationRouteRequest<Payload, Config> & Additions, res: EnvoyResponse<Partial<Config>>) => Result;
+  (req: EnvoyValidationRouteRequest<Payload, Config> & Additions, res: EnvoyResponse<Nullable<Partial<Config>>>) => Result;
 
 /**
  * Wraps any express.js-based handlers