Make chunk param of WritableStreamDefaultWriter.write and TransformStreamDefaultController.enqueue non-optional

[ikeyan]

Follow up #2425
The issue was first mentioned in #1682

Test script

This script demonstrates that calling enqueue() without arguments is behaviorally identical to enqueue(undefined). This confirms that allowing the omission of arguments in these methods poses a risk to type safety, unless the stream's generic type is explicitly defined to include undefined or void.

I successfully ran the script on Node.js v24.13.1, Chrome 145.0.7632.160, Firefox 148.0.2, Safari 26.3.1

function assert(condition, message) {
  if (!condition) {
    throw new Error("Assertion failed: " + message);
  }
}

async function runTests() {
  // === TransformStream Test ===
  const ts = new TransformStream({
    start(controller) {
      controller.enqueue();          // No arguments
      controller.enqueue(undefined); // Explicit undefined
    }
  });

  const reader = ts.readable.getReader();
  const tsResult1 = await reader.read();
  const tsResult2 = await reader.read();

  assert(tsResult1.value === undefined, "enqueue() should result in undefined");
  assert(tsResult2.value === undefined, "enqueue(undefined) should result in undefined");

  // === WritableStream Test ===
  const writtenChunks = [];
  const ws = new WritableStream({
    write(chunk) {
      writtenChunks.push(chunk); // Store written chunks for verification
    }
  });

  const writer = ws.getWriter();
  await writer.write();          // No arguments
  await writer.write(undefined); // Explicit undefined
  await writer.close();

  assert(writtenChunks[0] === undefined, "write() should write undefined");
  assert(writtenChunks[1] === undefined, "write(undefined) should write undefined");
  assert(writtenChunks.length === 2, "exactly 2 elements are written");
}

// Execute tests. If success, no output.
await runTests();

[github-actions]

Thanks for the PR!

This section of the codebase is owned by Kagami Sascha Rosylight (@saschanaz) - if they write a comment saying "LGTM" then it will be merged.

[Adam Naji (Bashamega)]

Please do not format the jsonc file, it creates extra diffs

[Kagami Sascha Rosylight (saschanaz)]

Thanks all! LGTM

[github-actions]

Merging because Kagami Sascha Rosylight (@saschanaz) is a code-owner of all the changes - thanks!