Update index.js

Author: dblythy

src/Adapters/Auth/index.js

@@ -137,7 +137,7 @@ function authDataValidator(provider, adapter, appIds, options) {
 
 function loadAuthAdapter(provider, authOptions) {
   // providers are auth providers implemented by default
-  let defaultAdapter = providers[provider] || {};
+  let defaultAdapter = providers[provider];
   // authOptions can contain complete custom auth adapters or
   // a default auth adapter like Facebook
   const providerOptions = authOptions[provider];
@@ -154,7 +154,7 @@ function loadAuthAdapter(provider, authOptions) {
     return;
   }
 
-  const adapter = Object.assign({}, defaultAdapter);
+  const adapter = defaultAdapter ?? Object.assign({});
   const keys = [
     'validateAuthData',
     'validateAppId',