fix: Fix AdapterService multi option when set to true (#1134)

Author: daffl

packages/adapter-commons/lib/service.js

@@ -11,7 +11,7 @@ const callMethod = (self, name, ...args) => {
 
 const checkMulti = (method, option) => {
   if (option === true) {
-    return;
+    return true;
   }
 
   return Array.isArray(option) ? option.includes(method) : false;

packages/adapter-commons/test/service.test.js

@@ -98,6 +98,15 @@ describe('@feathersjs/adapter-commons/service', () => {
           assert.strictEqual(error.message, 'Can not create multiple entries');
         });
     });
+
+    it('multi can be set to true', () => {
+      const service = new MethodService();
+
+      service.options.multi = true;
+
+      return service.create([])
+        .then(() => assert.ok(true));
+    });
   });
 
   it('filterQuery', () => {