fetchNextRow example

  #[\ReturnTypeWillChange]   public function next() {
    $this->currentSourceIds = NULL;
    $this->currentRow = NULL;

    // In order to find the next row we want to process, we ask the source     // plugin for the next possible row.     while (!isset($this->currentRow) && $this->getIterator()->valid()) {

      $row_data = $this->getIterator()->current() + $this->configuration;
      $this->fetchNextRow();
      $row = new Row($row_data, $this->getIds());

      // Populate the source key for this row.       $this->currentSourceIds = $row->getSourceIdValues();

      // Pick up the existing map row, if any, unless fetchNextRow() did it.       if (!$this->mapRowAdded && ($id_map = $this->idMap->getRowBySource($this->currentSourceIds))) {
        $row->setIdMap($id_map);
      }

      // Clear any previous messages for this row before potentially adding