How to simplify nested ifs

[Ozan Süel via Digitalmars-d-learn]

Hi

I have a construction like the following

if (source) {
  if (source.pool) {
    if (source.pool.repository) {
      if (source.pool.repository.directory) {
        if (source.pool.repository.directory.users) {
        return source.pool.repository.directory.users[ownerID];
                                                }
                                        }
                                }
                        }
                }