how can i save a pdf file in another history table?

i generate pdf in spring boot

  ProduitPDF produitPDF = new ProduitPDF();
    produitPDF.setId(Product.getId());
    produitPDF.setNameproduit(Product.getName());


    try {
        /*
        String pdfGenere = VelocityGenerator.generateHtmlPdf(produitPDF);
         htmlToPdfUtil.htmlToPdf(pdfGenere,"pdf")  ;
         */
        String pdfGenere = VelocityGenerator.generateHtmlPdf(produitPDF);
        String fileName = htmlToPdfUtil.htmlToPdf(pdfGenere, "pdf");
        Label.setCertificateOfApprovalOfTheLabel(fileName);

        labelRepository.save(Label);

i went to save fiche pdf in this attribut CertificateOfApprovalOfTheLabel but he give me null

History.setEventCertificationInCaseOfAgreementOrRenewal(product.getLabel().getCertificateOfApprovalOfTheLabel());