beamer中\end{frame}报错

\documentclass[10pt]{beamer}
\usepackage[space,hyperref,UTF8]{ctex}
\usetheme{Warsaw}
\usepackage{mathptmx}
\usefonttheme[onlymath]{serif}
\setbeamertemplate{navigation symbol}{}
\usepackage{amsmath}

\author[Lee]{Lawrence Lee}
\date{\today}
\title[练习]{Beamer练习}

\begin{document}
\frame{\titlepage}
\begin{frame}{Theme}
        contents\cite{001}
\end{frame}

\begin{frame}[allowframebreak]{References}
\def\newblock{}
\bibliographystyle{plain}
\bibliography{mybib}
\end{frame}
\end{document}

bib文件中的内容

@inproceedings{001,
author = {R. Guti\'{e}rrez-Cuevas and S. A. Wadood and A. N. Vamivakas and M. A. Alonso},
booktitle = {Frontiers in Optics / Laser Science},
journal = {Frontiers in Optics / Laser Science},
keywords = {Coherent states; Cylindrical lenses; Fractional Fourier transforms; Gaussian beams; Michelson interferometers; Spatial light modulators},
pages = {FW1B.4},
publisher = {Optical Society of America},
title = {Majorana Representation and Hidden Symmetries of Structured-Gaussian Beams},
year = {2020},
url = {http://www.osapublishing.org/abstract.cfm?URI=FiO-2020-FW1B.4},
doi = {10.1364/FIO.2020.FW1B.4}
}

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