code: protected function loadForeignDataItems()
      {
          if (!$this->fileSource) {
              \d("boom");
  
              return false;
          }
          $foreignModelClass = $this->foreignModelClass;
  
          $lines = $this->fileSource->getLines($this->lazyForeign);
          $lineCount = 0;
          foreach ($lines as $id => $line) {
              if ($this->lazyForeign) {
                  $this->createForeignDataItem(null, ['deferredModel' => $line]);
              } else {
                  $model = $this->createModel($line->id, $line->attributes);
                  $this->createForeignDataItem($model, ['deferredModel' => $line]);
              }
              $lineCount++;
          }
          $this->task->addInfo("Processed {$lineCount} lines from {$this->fileSource->id}");
      }
docs: Load the data items from the file source.
  
  @return bool|null False on fail, null on success (@todo change this to true)