• See PHI1981.
• See https://discourse.phabricator-community.org/t/unhandled-exception-error-call-to-a-member-function-setexternaluri-on-null/4538.

In D21511, I renamed the iterator variable in this loop from $path to $submodule_path, but incorrectly did not modify the $path->setExternalURI() call:

foreach ($submodules as $submodule_path) {     // <<< Renamed.
  $full_path = $submodule_path->getFullPath();
  $key = 'submodule.'.$full_path.'.url';
  if (isset($dict[$key])) {
    $path->setExternalURI($dict[$key]);        // <<< Now incorrect.
  }
}

This scope has a different variable named $path (which the rename was attempting to avoid clobbering), so the static analyzer reasonably couldn't detect this issue.

However, the existence of the original code might point at a bug in the "Variable Reused as Iterator" lint check: I would expect it to have prevented the original code in the first place.