def get_request(url: str) -> Tuple[bytes, bool]:
    resp = requests.get(url, allow_redirects=True)
    if not resp.ok:
        logger.error(f"Could not download file from {url}, server responded {resp.status_code}: {resp.reason}")
        return b"", False
    return resp.content, True

def merge_to_pdf(files: List, created_by: User, merged_name: str) -> Optional[File]:
    buffer = BytesIO()
    merger = PdfFileMerger()
    merged_filename = f"{merged_name}.pdf"

    if settings.BUILD_ENV == "local":
        for file in files:
            try:
                merger.append(file)  # here the error raises
            except PyPdfError:
                return None
    else:
        for file in files:
            pdf_content, ok = get_request(file)
            if not ok:
                return None
            pdf_buffer = BytesIO(pdf_content)
            try:
                merger.append(PdfFileReader(pdf_buffer))  # or here in non-local env
            except PyPdfError:
                return None

    merger.write(buffer)
    merger.close()
    buffer.seek(0)
    merged_file = File.objects.create(
        file=DjangoFile(buffer, merged_filename),
        name=merged_filename,
        created_by=created_by,
    )
    return merged_file