[Tables] Fix issue handling empty nextRowKey (Azure#20916)

* Fix issue handling undefined nextRowKey

* Address PR comments

* Add changelog

* remove export

* Address comments

sdk/tables/data-tables/CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Bugs Fixed
 
+- Fix issue when the Service returns an empty nextRowKey. [#20916](https://github.com/Azure/azure-sdk-for-js/pull/20916).
 - Fix issue with `getStatistics()` operation consistently failing and added test. [#20398](https://github.com/Azure/azure-sdk-for-js/pull/20398)
 
 ### Other Changes

sdk/tables/data-tables/src/utils/continuationToken.ts

@@ -3,28 +3,29 @@
 
 import { base64Decode, base64Encode } from "./bufferSerializer";
 
-export interface ContinuationToken {
+interface ContinuationToken {
   nextPartitionKey: string;
-  nextRowKey: string;
+  nextRowKey?: string;
 }
 
 /**
  * Encodes the nextPartitionKey and nextRowKey into a single continuation token
  */
 export function encodeContinuationToken(
-  nextPartitionKey: string = "",
-  nextRowKey: string = ""
+  nextPartitionKey?: string,
+  nextRowKey?: string
 ): string | undefined {
-  if (!nextPartitionKey && !nextRowKey) {
+  if (!nextPartitionKey) {
     return undefined;
   }
 
-  const continuationToken = JSON.stringify({
+  const continuationToken = {
     nextPartitionKey,
-    nextRowKey,
-  });
+    // Only add nextRowKey if the value is not null, undefined or empty string.
+    ...(nextRowKey && { nextRowKey }),
+  };
 
-  return base64Encode(continuationToken);
+  return base64Encode(JSON.stringify(continuationToken));
 }
 
 /**

sdk/tables/data-tables/test/internal/continuationToken.spec.ts

@@ -0,0 +1,43 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+import {
+  decodeContinuationToken,
+  encodeContinuationToken,
+} from "../../src/utils/continuationToken";
+
+import { assert } from "chai";
+
+describe("continuation token utils", () => {
+  it("should encode nextPartitionKey and nextRowKey", () => {
+    const encoded = encodeContinuationToken("foo", "bar");
+    assert.equal(encoded, "eyJuZXh0UGFydGl0aW9uS2V5IjoiZm9vIiwibmV4dFJvd0tleSI6ImJhciJ9");
+  });
+
+  it("should not encode nextRowKey if it is empty string", () => {
+    const encoded = encodeContinuationToken("foo", "");
+    assert.deepEqual(decodeContinuationToken(encoded!), { nextPartitionKey: "foo" });
+  });
+
+  it("should encode nextPartitionKey and undefined nextRowKey", () => {
+    const encoded = encodeContinuationToken("foo");
+    assert.equal(encoded, "eyJuZXh0UGFydGl0aW9uS2V5IjoiZm9vIn0=");
+  });
+
+  it("should return undefined if nextPartitionKey and nextRowKey are empty", () => {
+    const encoded = encodeContinuationToken();
+    assert.equal(encoded, undefined);
+  });
+
+  it("should decode nextPartitionKey and nextRowKey", () => {
+    const decoded = decodeContinuationToken(
+      "eyJuZXh0UGFydGl0aW9uS2V5IjoiZm9vIiwibmV4dFJvd0tleSI6ImJhciJ9"
+    );
+    assert.deepEqual(decoded, { nextPartitionKey: "foo", nextRowKey: "bar" });
+  });
+
+  it("should decode nextPartitionKey and undefined nextRowKey", () => {
+    const decoded = decodeContinuationToken("eyJuZXh0UGFydGl0aW9uS2V5IjoiZm9vIn0=");
+    assert.deepEqual(decoded, { nextPartitionKey: "foo" } as any);
+  });
+});