Wrong message error, while trying to adapt multiple overlaid rectangles as TikZ node code

Question

I'm trying to adapt this question's answer to my code.

The problem is that it doesn't compile, and the message error is strange:

LaTeX Error: Something's wrong--perhaps a missing \item.

For the line where we have \end{frame}, below.

Here's my code:

    \documentclass{beamer}
\mode<presentation> {
\usetheme{AnnArbor}
\usecolortheme{beaver}
}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{booktabs}
\usepackage{graphicx}



\usepackage{tikz}
\usetikzlibrary{arrows.meta,
                % automata,
                % chains,
                decorations.pathreplacing, 
                calligraphy,% had to be load after decorations.pathreplacing
                positioning,
                shapes,
                shadows,
                arrows}

\begin{document}
\begin{frame}
    \begin{figure}
            \begin{tikzpicture}[
                node distance=2cm, 
                multiple/.style = {
                    double copy shadow={
                        shadow xshift=1ex,shadow yshift=-1.5ex,
                        draw=black!30
                    },
                    fill=white,draw=black,thick
                },
                % ordinary/.style = {rectangle,draw,thick}
            ]
                \node[multiple, label={\small Source Files}] (source_files) {
                    import math\\
                    result = math.exp(1)\\
                    print("math.exp(1):", result)\\
                    \dots
                };
                \node[multiple, label={\small Object Files}] (object_files) [right=of source_files] {
                    00000100010\\
                    01010100111\\
                    01110010110\\
                    \dots
                };
                \node[ordinary, label={\small Executable Files}] (exec_files) [right=of object_files] {
                    00000100010\\
                    01010100111\\
                    01110010110\\
                    \dots
                };                
                % Arrows
                \draw[-{Latex[length=3mm, width=2mm]}, thick] (source_files) -- (object_files) node[midway, above] {Compiler};
                \draw[-{Latex[length=3mm, width=2mm]}, thick] (object_files) -- (exec_files) node[midway, above] {Linker};    
            \end{tikzpicture}
        \caption{From Assembly to machine executable instructions.}
        \label{High Level}
    \end{figure}

\end{frame}

\end{document}

Answer 1

The code compiles without error if an align option is given to the nodes. For example, if align=left, is placed after each occurrence of \node[.