Doclet failes with StringIndexOutOfBoundsException

[olegshtch]

I'm trying to generate documentation and gets error with version 1.0.0 published on the Central:

javadoc: error - In doclet class info.leadinglight.umljavadoclet.UmlJavaDoclet,  method start has thrown an exception java.lang.reflect.InvocationTargetException
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
    at java.lang.String.substring(String.java:1967)
    at info.leadinglight.umljavadoclet.model.ModelPackage.parentPackageFullName(ModelPackage.java:62)
    at info.leadinglight.umljavadoclet.model.Model.isRootPackage(Model.java:87)
    at info.leadinglight.umljavadoclet.model.Model.rootPackages(Model.java:75)
    at info.leadinglight.umljavadoclet.printer.OverviewDiagramPrinter.generate(OverviewDiagramPrinter.java:20)
    at info.leadinglight.umljavadoclet.UmlJavaDoclet.generateOverviewDiagram(UmlJavaDoclet.java:173)
    at info.leadinglight.umljavadoclet.UmlJavaDoclet.start(UmlJavaDoclet.java:75)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.sun.tools.javadoc.DocletInvoker.invoke(DocletInvoker.java:310)
    at com.sun.tools.javadoc.DocletInvoker.start(DocletInvoker.java:189)
    at com.sun.tools.javadoc.Start.parseAndExecute(Start.java:366)
    at com.sun.tools.javadoc.Start.begin(Start.java:219)
    at com.sun.tools.javadoc.Start.begin(Start.java:205)
    at com.sun.tools.javadoc.Main.execute(Main.java:64)
    at com.sun.tools.javadoc.Main.main(Main.java:54)

[gboersma]

Merged the pull request.