lib: fix no response event on null in continue request

When sending a continue request, server response with null,
it does not fires the response event type

Fixes: nodejs#38258

lib/internal/http2/compat.js

@@ -760,7 +760,9 @@ class Http2ServerResponse extends Stream {
     }
 
     if (chunk !== null && chunk !== undefined)
-      this.write(chunk, encoding);
+      chunk = '';  
+
+    this.write(chunk, encoding);
 
     state.headRequest = stream.headRequest;
     state.ending = true;

test/parallel/test-http2-compat-expect-continue.js

@@ -6,49 +6,90 @@ if (!common.hasCrypto)
 const assert = require('assert');
 const http2 = require('http2');
 
-const testResBody = 'other stuff!\n';
+{
+  const testResBody = 'other stuff!\n';
 
-// Checks the full 100-continue flow from client sending 'expect: 100-continue'
-// through server receiving it, sending back :status 100, writing the rest of
-// the request to finally the client receiving to.
+  // Checks the full 100-continue flow from client sending 'expect: 100-continue'
+  // through server receiving it, sending back :status 100, writing the rest of
+  // the request to finally the client receiving to.
 
-const server = http2.createServer();
+  const server = http2.createServer();
 
-let sentResponse = false;
+  let sentResponse = false;
 
-server.on('request', common.mustCall((req, res) => {
-  res.end(testResBody);
-  sentResponse = true;
-}));
+  server.on('request', common.mustCall((req, res) => {
+    res.end(testResBody);
+    sentResponse = true;
+  }));
+
+  server.listen(0);
+
+  server.on('listening', common.mustCall(() => {
+    let body = '';
 
-server.listen(0);
+    const client = http2.connect(`http://localhost:${server.address().port}`);
+    const req = client.request({
+      ':method': 'POST',
+      'expect': '100-continue'
+    });
 
-server.on('listening', common.mustCall(() => {
-  let body = '';
+    let gotContinue = false;
+    req.on('continue', common.mustCall(() => {
+      gotContinue = true;
+    }));
 
-  const client = http2.connect(`http://localhost:${server.address().port}`);
-  const req = client.request({
-    ':method': 'POST',
-    'expect': '100-continue'
-  });
+    req.on('response', common.mustCall((headers) => {
+      assert.strictEqual(gotContinue, true);
+      assert.strictEqual(sentResponse, true);
+      assert.strictEqual(headers[':status'], 200);
+      req.end();
+    }));
 
-  let gotContinue = false;
-  req.on('continue', common.mustCall(() => {
-    gotContinue = true;
+    req.setEncoding('utf8');
+    req.on('data', common.mustCall((chunk) => { body += chunk; }));
+    req.on('end', common.mustCall(() => {
+      assert.strictEqual(body, testResBody);
+      client.close();
+      server.close();
+    }));
   }));
+}
+
+{
+  // Checks the full 100-continue flow from client sending 'expect: 100-continue'
+  // through server receiving it and ending the request.
+
+  const server = http2.createServer();
 
-  req.on('response', common.mustCall((headers) => {
-    assert.strictEqual(gotContinue, true);
-    assert.strictEqual(sentResponse, true);
-    assert.strictEqual(headers[':status'], 200);
-    req.end();
+  server.on('request', common.mustCall((req, res) => {
+    res.end();
   }));
 
-  req.setEncoding('utf8');
-  req.on('data', common.mustCall((chunk) => { body += chunk; }));
-  req.on('end', common.mustCall(() => {
-    assert.strictEqual(body, testResBody);
-    client.close();
-    server.close();
+  server.listen(0);
+
+  server.on('listening', common.mustCall(() => {
+    const client = http2.connect(`http://localhost:${server.address().port}`);
+    const req = client.request({
+      ":path": "/",
+      'expect': '100-continue'
+    });
+
+    let gotContinue = false;
+    req.on('continue', common.mustCall(() => {
+      gotContinue = true;
+    }));
+
+    let gotResponse = false;
+    req.on('response', common.mustCall(() => {
+      gotResponse = true;
+    }));
+
+    req.setEncoding('utf8');
+    req.on('end', common.mustCall(() => {
+      assert.strictEqual(gotContinue, true);
+      assert.strictEqual(gotResponse, true);
+      client.close();
+      server.close();
+    }));
   }));
-}));
+}