LaTeX 错误：cls 文件中缺少 \begin{document}

Question

错误信息：

kpathsea: Running mktexmf SimSun
! I can't find file `SimSun'.
<*> ...:=ljfour; mag:=1; nonstopmode; input SimSun
                                                  
Please type another input file name
! Emergency stop.
<*> ...:=ljfour; mag:=1; nonstopmode; input SimSun
                                                  
Transcript written on mfput.log.
grep: SimSun.log: No such file or directory
mktextfm: `mf-nowin -progname=mf \mode:=ljfour; mag:=1; nonstopmode; input SimSun' failed to make SimSun.tfm.
kpathsea: Appending font creation commands to missfont.log.


./thuthesis.cls:687: LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.687     }
           
No pages of output.

有关错误的源代码(.cls l.687)：

\newcommand\thu@mac@word@font@path{%
  /Applications/Microsoft Word.app/Contents/Resources/DFonts/%
}
\ifthu@fontset@auto
  \ifthu@system@windows
    \thusetup{fontset = windows}
  \else
    \IfFontExistsTF{SimSun}{
      \thusetup{fontset = windows}
    }{
      \IfFileExists{\thu@mac@word@font@path/SimSun.ttf}{
        \thusetup{fontset = windows}
      }{
        \ifthu@system@mac
          \thusetup{fontset = mac}
        \else
          \IfFontExistsTF{Noto Serif CJK SC}{
            \thusetup{fontset = ubuntu}
          }{
            \thusetup{fontset = fandol}
          }
        \fi
      }
    } % l.687
  \fi
\fi

我还没有学过tex。但是我使用的cls文件中的这段代码告诉它，如果找到SimSun.ttf，字体集将是windows。

不知道这个错误是不是跟有关I can't find file SimSun.，平台是mac，不过SimSun.ttf确实存在，路径是/Applications/Microsoft Word.app/Contents/Resources/DFonts/SimSun.ttf。

至于fontspec，thuthesis.cls中的代码：

\PassOptionsToPackage{no-math}{fontspec}

我认为该错误与 tex 文件无关。其内容：

\documentclass[degree=master]{thuthesis}

\input{thusetup}


\begin{document}

\maketitle

\input{data/committee}

\copyrightpage

\frontmatter
\input{data/abstract}

\tableofcontents


\input{data/denotation}


\mainmatter
\input{data/chap01}
\input{data/chap02}
\input{data/chap03}
\input{data/chap04}

\backmatter

\appendix
\input{data/appendix}

\input{data/acknowledgements}

\statement

\input{data/resume}

\input{data/comments}

\input{data/resolution}

\end{document}

我使用 xelatex 进行编译。发行版本是

XeTeX 3.14159265-2.6-0.99999 (TeX Live 2018)
kpathsea version 6.3.0