repl: avoid crashing from null and undefined errors

When `throw undefined` or `throw null` is executed, the REPL crashes.
This change does a check for `null|undefined` before accessing an
error's properties to prevent crashing.

Fixes: https://github.com/nodejs/node/issues/16545
Fixes: https://github.com/nodejs/node/issues/16607

PR-URL: https://github.com/nodejs/node/pull/16574
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Lance Ball <lball@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

lib/repl.js

@@ -257,12 +257,13 @@ function REPLServer(prompt,
         }
       } catch (e) {
         err = e;
-        if (err.message === 'Script execution interrupted.') {
+
+        if (err && err.message === 'Script execution interrupted.') {
           // The stack trace for this case is not very useful anyway.
           Object.defineProperty(err, 'stack', { value: '' });
         }
 
-        if (err && process.domain) {
+        if (process.domain) {
           debug('not recoverable, send to domain');
           process.domain.emit('error', err);
           process.domain.exit();

test/parallel/test-repl-throw-null-or-undefined.js

@@ -0,0 +1,18 @@
+'use strict';
+require('../common');
+
+// This test ensures that the repl does not
+// crash or emit error when throwing `null|undefined`
+// ie `throw null` or `throw undefined`
+
+const assert = require('assert');
+const repl = require('repl');
+
+const r = repl.start();
+
+assert.doesNotThrow(() => {
+  r.write('throw null\n');
+  r.write('throw undefined\n');
+}, TypeError, 'repl crashes/throw error on `throw null|undefined`');
+
+r.write('.exit\n');