tls: null not valid as a renegotiate callback

Allow undefined as a callback, but do not allow null.

PR-URL: #25929
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_tls_wrap.js

@@ -601,7 +601,7 @@ TLSSocket.prototype._init = function(socket, wrap) {
 TLSSocket.prototype.renegotiate = function(options, callback) {
   if (options === null || typeof options !== 'object')
     throw new ERR_INVALID_ARG_TYPE('options', 'Object', options);
-  if (callback != null && typeof callback !== 'function')
+  if (callback !== undefined && typeof callback !== 'function')
     throw new ERR_INVALID_CALLBACK();
 
   if (this.destroyed)

test/parallel/test-tls-disable-renegotiation.js

@@ -63,6 +63,12 @@ server.listen(0, common.mustCall(() => {
       type: TypeError,
     });
 
+    common.expectsError(() => client.renegotiate({}, null), {
+      code: 'ERR_INVALID_CALLBACK',
+      type: TypeError,
+    });
+
+
     // Negotiation is still permitted for this first
     // attempt. This should succeed.
     let ok = client.renegotiate(options, common.mustCall((err) => {