Empty array schema should have items property

Author: mohsen1

src/index.js

@@ -45,6 +45,7 @@ function convert (json, options = {}) {
     let schema = {type: 'array'};
 
     if (!json.length) {
+      schema.items = {};
       return schema;
     }
 

test/primitives.js

@@ -32,7 +32,7 @@ describe('primitives', ()=> {
   });
 
   describe('empty array', ()=> {
-    expect([], {type: 'array'});
+    expect([], {type: 'array', items: {}});
   });
 
   describe('empty object', ()=> {