🐛 Fixed excerpt property being missing if plaintext is NULL or ""

closes https://github.com/TryGhost/Ghost/issues/10558
- added conditional to explicitly set `excerpt` to `null` in the API output serializer when a post has no `plaintext` or `custom_excerpt` value

core/server/api/v2/utils/serializers/output/utils/extra-attrs.js

@@ -8,6 +8,8 @@ module.exports.forPost = (frame, model, attrs) => {
 
             if (plaintext) {
                 attrs.excerpt = plaintext.substring(0, 500);
+            } else {
+                attrs.excerpt = null;
             }
         } else {
             attrs.excerpt = attrs.custom_excerpt;

core/test/unit/api/v2/utils/serializers/output/utils/extra-attrs_spec.js

@@ -33,5 +33,17 @@ describe('Unit: v2/utils/serializers/output/utils/extra-attrs', () => {
 
             attrs.excerpt.should.eql(new Array(501).join('A'));
         });
+
+        it('has excerpt when plaintext is null', () => {
+            model.get.withArgs('plaintext').returns(null);
+
+            const attrs = {};
+
+            extraAttrsUtil.forPost(frame, model, attrs);
+            model.get.called.should.be.true();
+
+            attrs.should.have.property('excerpt');
+            (attrs.excerpt === null).should.be.true();
+        });
     });
 });