private String toPackageName(String className) {
        int packageEndIndex = className.lastIndexOf('.');
        if (packageEndIndex > 0) {
            return className.substring(0, packageEndIndex);
        }
        return null;
    }
Names of resources that could not be found. Used to avoid repeated
lookup of commonly accessed, but often not present, resources like
<code>META-INF/services/javax.xml.parsers.SAXParserFactory</code>.
tika-core/src/main/java/org/apache/tika/fork/ClassLoaderProxy.java