chore(core) Document: add test checking pageContents empty string behavior (#2836)

Co-authored-by: Ben Burns <[email protected]>

Author: skarard

langchain-core/src/documents/tests/document.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, test } from "@jest/globals";
+import { Document } from "../document.js";
+
+describe("Document", () => {
+  test("Constructing a document with an empty sting", async () => {
+    const doc = new Document({ pageContent: "" });
+    expect(doc.pageContent).toEqual("");
+  });
+
+  test("Constructing a document with an undefined at runtime", async () => {
+    const pageContent = undefined as unknown as string;
+    const doc = new Document({ pageContent });
+    expect(doc.pageContent).toEqual("");
+  });
+});