How to write plugin that adds resolve.extensions when it is not defined in config?

[krutoo]

Hi, im trying to write simple plugin that adds extensions in configuration.

I write this in my plugin:

compiler.hooks.afterEnvironment.tap('MyPlugin', () => {
  if (resolveExtensions !== false) {
    if (!compiler.options.resolve.extensions) {
      compiler.options.resolve.extensions = [];
    }

    for (const ext of resolveExtensions) {
      if (compiler.options.resolve.extensions.includes(ext)) {
        continue;
      }

      compiler.options.resolve.extensions.push(ext);
    }
  }
});

Its working only when extensions provided in configuration object. Even if empty array is provided.

It is not working if resolve.extensions is not defined.

Is it bug or do I something wrong?