java.lang.IllegalArgumentException: URI is not hierarchical when run jhindexer

Question

I need to generate a help system for my application using the JavaHelp package. I have downloaded the project from the github repository and I have compiled it both with the GNU make tool and with Apache ant on a JDK 1.8. I have managed to generate my help system.

The problem comes from using the jhindexer tool to generate the database of terms to perform searches. According to the documentation simply execute in script or directly jar jhindexer and you indicate the directory where the .html files are located.

When executing the tool I get the following error:

 ~/Downloads: jhindexer JavaHelp
    Exception in thread "main" java.lang.IllegalArgumentException: URI is not hierarchical
        at java.io.File.<init>(File.java:418)
        at com.sun.java.help.search.RAFFileFactory.get(RAFFileFactory.java:87)
        at com.sun.java.help.search.BlockManager.<init>(BlockManager.java:87)
        at com.sun.java.help.search.BtreeDict.init(BtreeDict.java:212)
        at com.sun.java.help.search.FullBtreeDict.<init>(FullBtreeDict.java:343)
        at com.sun.java.help.search.DefaultIndexBuilder.<init>(DefaultIndexBuilder.java:79)
        at com.sun.java.help.search.Indexer.compile(Indexer.java:197)
        at com.sun.java.help.search.Indexer.main(Indexer.java:86)

The error occurs in this line, I tried to make changes but I can not get them to be applied in the final compilation.

if (isFileURL(url)) {
    try {
    File f = new File(url.toURI());

    // refactor so it runs with verification on...

    // Object o = new FilePermission(f, update ? "write":"read");
    // here -- check if AccessController.checkPermission(p);

    result =  new RAFFile(f, update);
    debug ("Opened Dict file with file protocol:" +  f);
    } catch (SecurityException e) {
    // cannot do "it" -- code is not yet in place
    } catch (URISyntaxException x) {
        throw (IOException) new IOException(x.toString()).initCause(x);
    }

I have compiled against a JDK 1.6 and the same error also occurs. Does anyone know how I can operate this tool? Thank you so much.