TypeError: array_keys(): Argument #1 ($array) must be of type array, null given in array_keys()

Also see this commit: a9d7e755c7c45ec3d6baabbf3c77b328fc72a25f

    // If there is no views data then quit (does this happen?).
    if (count($parentData) === 0) {
      return $data;
    }
    $originalTable = $parentData[$fieldTableName];

$originalTable can be NULL.

Sorry, I did not discuss this on IRC, write a test for this.
This change is so small I just put it out here as it fixes my problem. Hope this helps others.

How is this possible though? What is the definition and table?

Are you sure something isnt malformed or altered elsewhere?

Issue template needs to be fixed.