repl: fix eval return value

In case no error has occurred during the evaluation of some code,
`undefined` has been returned in some cases as error argument instead
of `null`. This is fixed by this patch.

PR-URL: #25731
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

lib/repl.js

@@ -216,10 +216,11 @@ function REPLServer(prompt,
  }
 
  function defaultEval(code, context, file, cb) {
- var err, result, script, wrappedErr;
- var wrappedCmd = false;
- var awaitPromise = false;
- var input = code;
+ let result, script, wrappedErr;
+ let err = null;
+ let wrappedCmd = false;
+ let awaitPromise = false;
+ const input = code;
 
  if (/^\s*\{/.test(code) && /\}\s*$/.test(code)) {
  // It's confusing for `{ a : 1 }` to be interpreted as a block
@@ -363,7 +364,7 @@ function REPLServer(prompt,
  }
 
  promise.then((result) => {
- finishExecution(undefined, result);
+ finishExecution(null, result);
  }, (err) => {
  if (err && process.domain) {
  debug('not recoverable, send to domain');