feat: 🎸 not make jsonld tags when jsonld method returns null

✅ Closes: #23

Author: Ryota Yamamoto

Diff for: src/createMixin.ts

@@ -33,6 +33,10 @@ export default (options: Options = {}): JsonldMixin => {
         return {};
       }
 
+      if (this.$options.jsonld.call(this) === null) {
+        return {};
+      }
+
       const stringifiedJson = JSON.stringify(this.$options.jsonld.call(this), null, mergedOptions.space);
       const innerHTML = mergedOptions.space === 0 ? stringifiedJson : `\n${stringifiedJson}\n`;
 

Diff for: test/createMixin.spec.js

@@ -89,6 +89,12 @@ describe('with jsonld', () => {
     });
   });
 
+  test('head method returns an empty object when jsonld returns null', () => {
+    const mock = mockInstanceFactory();
+    mock.$options.jsonld = () => null;
+    expect(mock.$options.head.call(mock)).toEqual({});
+  })
+
   describe('customizing indentation', () => {
     test('using tab', () => {
       const mock = mockInstanceFactory({ space: '\t' });