Don't add an undefined id to the span for marked content

It fixes #20102.

src/display/text_layer.js

@@ -290,7 +290,7 @@ class TextLayer {
           const parent = this.#container;
           this.#container = document.createElement("span");
           this.#container.classList.add("markedContent");
-          if (item.id !== null) {
+          if (item.id) {
             this.#container.setAttribute("id", `${item.id}`);
           }
           parent.append(this.#container);

test/integration/accessibility_spec.mjs

@@ -281,4 +281,25 @@ describe("accessibility", () => {
       );
     });
   });
+
+  describe("No undefined id", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait("issue20102.pdf", ".textLayer");
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    it("must check that span hasn't an 'undefined' id", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          const id = await page.$eval("span.markedContent", span => span.id);
+          expect(id).withContext(`In ${browserName}`).toBe("");
+        })
+      );
+    });
+  });
 });

test/pdfs/.gitignore

@@ -732,3 +732,4 @@
 !bug1974436.pdf
 !firefox_logo.pdf
 !issue20062.pdf
+!issue20102.pdf