Should overwriting child_process.execFile result in changed behaviour of child_process.exec?

[Ginden]

node -e "child_process.execFile = null; child_process.exec('cat package.json')"
    child_process.js:138
      return exports.execFile(opts.file,
    TypeError: exports.execFile is not a function
        at Object.exports.exec (child_process.js:138:18)

I couldn't find in documentation why child_process behave this way (but it behaves like that for at least four years).

Relevant line https://github.com/nodejs/node/blob/58831b2/lib/child_process.js#L136

[bnoordhuis]

I don't think we consider this a bug; I'll interpret the fact that this issue didn't generate discussion as tacit approval of that. If you monkey-patch node.js itself, unexpected things may happen.

I'll close this out, reopen if that is a mistake.