biblatex 不显示部分

Question

在我的 biblatex 配置中，我为图像添加了另一个部分。

这是我目前的代码：

\newcommand{\@bibtitle}{Quellenverzeichnis}
\newcommand{\@bibtitleLiteratur}{Literatur}
\newcommand{\@bibtitleAvmedia}{Filme und audiovisuelle Medien}
\newcommand{\@bibtitleOnline}{Online-Quellen}   
\newcommand{\@bibtitleImage}{Visuelle und graphische Medien}
\defbibfilter{literature}{
    not ( type=movie or type=video or type=image or type=music or type=audio or type=online or type=electronic or type=www or type=software )}   
\defbibfilter{avmedia}{
    ( type=movie or type=video or type=music or type=audio or type=software )}   
\defbibfilter{online}{
    ( type=online or type=electronic or type=www )}    
\defbibfilter{image}{
    ( type=image)}
%some other code
\newcommand{\MakeBibliography}[1][]{
    \clearpage
    \ifthenelse{\equal{#1}{nosplit}}
        {
            \printbibheading[heading=bibintoc,title={\@bibtitle}]
            \begin{bibhyphenation}  
            \printbibliography[heading=noheader]
            \end{bibhyphenation}
        }
        {
            \printbibheading[heading=bibintoc,title={\@bibtitle}]
            \begin{bibhyphenation}
            \printbibliography[filter=literature,heading=subbibintoc,title={\@bibtitleLiteratur}]
            \printbibliography[filter=avmedia,heading=subbibintoc,title={\@bibtitleAvmedia}]
            \printbibliography[filter=image,heading=subbibintoc,title={\@bibtitleImage}]
            \printbibliography[filter=online,heading=subbibintoc,title={\@bibtitleOnline}]
            \end{bibhyphenation}
        }
}

然而，如果我宣布

@image{pr_tabelle,
    url={http://de.onpage.org/wiki/images/2/29/PageRank2.jpg}
}

它没有显示在参考书目中，而

@online{explorer,
author={{Siddharth}},
title={9 Most Common IE Bugs and How to Fix Them},
year={2009},
url={http://code.tutsplus.com/tutorials/9-most-common-ie-bugs-and-how-to-fix-them--net-7764}
}

看起来没什么问题。