public function columns($columnName, $label = null)
{
if (!is_string($columnName)) {
throw new \InvalidArgumentException('$columnName must be set');
}
if ($this->resetColumns) {
$this->columns = [];
$this->resetColumns = false;
}
if (is_null($label)) {
$label = $columnName;
}
$this->columns[$columnName] = $label;
return $this;
}