TCPDF Transaction: Empty font family - php

Question

I am using TCPDF to generate a PDF and I get the following error when i use transaction:
TCPDF ERROR: Empty font family
I have the following code snippet(with transaction for pagebreak):
$titleDesc = $sPDFQuestion;
$pageNum = $this->pdf->PageNo();
$this->pdf->startTransaction();
$this->pdf->Bookmark($sPDFQuestion, 1, 0);
$this->pdf->titleintopdf($pdfTitle, $sPDFQuestion);
if($pageNum != $this->pdf->PageNo()){
$this->pdf->rollbackTransaction(false);
$this->pdf->AddPage('P', 'A4');
$this->pdf->Bookmark($sPDFQuestion, 1, 0);
$this->pdf->titleintopdf($pdfTitle, $sPDFQuestion);
}
else {
$this->pdf->commitTransaction();
}
This is the function titleintopdf():
public function titleintopdf($title, $description = '')
{
if (!empty($title)) {
$title = $this->delete_html($title);
$oldsize = $this->FontSizePt;
$this->SetFontSize($oldsize + 4);
$this->Line(5, $this->y, ($this->w - 5), $this->y);
$this->ln(3);
$this->MultiCell('', '', $title, '', 'C', 0);
$this->MultiCell('', '', "Number:".$this->PageNo(), '', 'C', 0);
if (!empty($description) && isset($description)) {
$description = $this->delete_html($description);
$this->ln(7);
$this->SetFontSize($oldsize + 2);
$this->MultiCell('', '', $description, '', 'C', 0);
$this->ln(2);
} else {
$this->ln(4);
}
$this->MultiCell('', '', "Number:".$this->PageNo(), '', 'C', 0);
$this->Line(5, $this->y, ($this->w - 5), $this->y);
$this->ln(5);
$this->SetFontSize($oldsize);
}
}
When I don't rollback the transaction and I just commit it instead, everything works fine. I don't have a clue, why this error occurs. Do you know what the problem could be?
Greets!

Answer 1

The error lies in
$this->pdf->rollbackTransaction(false);
'false' means here to not restore $this->pdf to its original state, but to return the original state as a TCPDF object, so correct would be either:
$this->pdf = $this->pdf->rollbackTransaction(false);
or
$this->pdf->rollbackTransaction(true);
The error "TCPDF ERROR: Empty font family" is just a follow-up error of $this->pdf not being valid anymore.