fix: Email for document update can include empty diff block

server/emails/templates/DocumentPublishedOrUpdatedEmail.tsx

@@ -76,12 +76,14 @@ export default class DocumentPublishedOrUpdatedEmail extends BaseEmail<
         });
 
         // inline all css so that it works in as many email providers as possible.
-        body = await inlineCss(content, {
+        body = content
+          ? await inlineCss(content, {
               url: env.URL,
               applyStyleTags: true,
               applyLinkTags: false,
               removeStyleTags: true,
-        });
+            })
+          : undefined;
       }
     }
 

server/models/helpers/DocumentHelper.test.ts

@@ -113,6 +113,25 @@ same on both sides`,
       expect(html).not.toContain("this is a highlight");
     });
 
+    it("should return undefined if no diff is renderable", async () => {
+      const before = new Revision({
+        title: "Title",
+        text: `
+This is a test paragraph`,
+      });
+
+      const after = new Revision({
+        title: "Title",
+        text: `
+This is a [test paragraph](https://example.net)`,
+      });
+
+      // Note: This test may fail in the future when support for diffing marks
+      // is improved.
+      const html = await DocumentHelper.toEmailDiff(before, after);
+      expect(html).toBeUndefined();
+    });
+
     it("should trim table rows to show minimal diff including header", async () => {
       const before = new Revision({
         title: "Title",

server/models/helpers/DocumentHelper.tsx

@@ -195,6 +195,13 @@ export default class DocumentHelper {
     const containsDiffElement = (node: Element | null) =>
       node && node.innerHTML.includes("data-operation-index");
 
+    // The diffing lib isn't able to catch all changes currently, e.g. changing
+    // the type of a mark will result in an empty diff.
+    // see: https://github.com/tnwinc/htmldiff.js/issues/10
+    if (!containsDiffElement(doc.querySelector("#content"))) {
+      return;
+    }
+
     // We use querySelectorAll to get a static NodeList as we'll be modifying
     // it as we iterate, rather than getting content.childNodes.
     const contents = doc.querySelectorAll("#content > *");