pgfkeys error: I do not know the key '/tikz/folder/.pic'

Question

I try to use anwser, but when I compile, it output:

! Package pgfkeys Error: I do not know the key '/tikz/folder/.pic' and I am going to ignore it. Perhaps you misspelled it.

Here is my code:

\documentclass[xcolor=x11names,compress]{beamer}
\usepackage{forest}


\definecolor{folderbg}{RGB}{124,166,198}
\definecolor{folderborder}{RGB}{110,144,169}

\def\Size{4pt}
\tikzset{
    folder/.pic={
        \filldraw[draw=folderborder,top color=folderbg!50,bottom color=folderbg]
        (-1.05*\Size,0.2\Size+5pt) rectangle ++(.75*\Size,-0.2\Size-5pt);  
        \filldraw[draw=folderborder,top color=folderbg!50,bottom color=folderbg]
        (-1.15*\Size,-\Size) rectangle (1.15*\Size,\Size);
    }
}

\begin{document}

\begin{frame}{forest test}
    \begin{forest}
        for tree={
            font=\ttfamily,
            grow'=0,
            child anchor=west,
            parent anchor=south,
            anchor=west,
            calign=first,
            inner xsep=7pt,
            edge path={
                \noexpand\path [draw, \forestoption{edge}]
                (!u.south west) +(7.5pt,0) |- (.child anchor) pic {folder} \forestoption{edge label};
            },
            before typesetting nodes={
                if n=1
                {insert before={[,phantom]}}
                {}
            },
            fit=band,
            before computing xy={l=15pt},
        }  
        [system
            [config
            ]
            [lib
                [Access
                ]
                [Plugin
                ]
            ]
            [templates
            ]
            [tests
            ]
        ]
    \end{forest}
\end{frame}

\end{document}

Here is my package info:

Package: tikz 2010/10/13 v2.10 (rcs-revision 1.76）
Package: forest 2013/10/17 v1.04 Drawing (linguistic) trees