tls: permit null as a cipher value

Allow null along with undefined for cipher value.

Fixes: nodejs#36292

PR-URL: nodejs#36318
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

lib/_tls_common.js

@@ -263,7 +263,7 @@ exports.createSecureContext = function createSecureContext(options) {
     }
   }
 
-  if (ciphers !== undefined)
+  if (ciphers != null)
     validateString(ciphers, 'options.ciphers');
 
   // Work around an OpenSSL API quirk. cipherList is for TLSv1.2 and below,

test/parallel/test-tls-set-ciphers.js

@@ -104,3 +104,7 @@ test('AES256-SHA', ':', U, U, 'ERR_INVALID_ARG_VALUE');
 // Using '' is synonymous for "use default ciphers"
 test('TLS_AES_256_GCM_SHA384', '', 'TLS_AES_256_GCM_SHA384');
 test('', 'TLS_AES_256_GCM_SHA384', 'TLS_AES_256_GCM_SHA384');
+
+// Using null should be treated the same as undefined.
+test(null, 'AES256-SHA', 'AES256-SHA');
+test('AES256-SHA', null, 'AES256-SHA');