Python: 複数PDFを結合して１つのPDFに変換する

from io import BytesIO
from typing import List
import PyPDF2

def merge_pdfs(pdf_bytes: List[bytes]) -> bytes:
    merger: PyPDF2.PdfFileMerger = PyPDF2.PdfFileMerger()
    try:
        for b in pdf_bytes:
            merger.append(PyPDF2.PdfFileReader(BytesIO(b))) if b else None
        ret: BytesIO = BytesIO()
        merger.write(ret)
        ret.seek(0)
        return ret.read()
    finally:
        merger.close()

bytes <-> File読み書きは割愛。