The JavaFX-Class-Path attribute is obsolete, the packager should stop using it.

Consider a call to packager like that:

        <fx:jar destfile="${dist.dir}/unsigned/App.jar">
            <fx:application refid="com.company.app.name"/>
            <fx:platform refid="myPlatform"/>
            <fileset dir="${build.classes.dir}"/>
            <fx:resources>
                <fx:fileset dir="${basedir}/${dist.dir}/signed"
                            includes="Kit.jar"/>
            </fx:resources>
            <manifest>
                <attribute name="Implementation-Title" value="${application.title}"/>
                <attribute name="Implementation-Vendor" value="${application.vendor}"/>
                <attribute name="Implementation-Version" value="${application.version.extended}"/>
            </manifest>
        </fx:jar>

As a consequence the manifest of App.jar contains the JavaFX-Class-Path attribute:

Manifest-Version: 1.0
Created-By: JavaFX Packager
JavaFX-Application-Class: com.whatever.App
Main-Class: com/javafx/main/Main
JavaFX-Version: 8.0+
Implementation-Title: My Title
Implementation-Version: 1.0
Implementation-Vendor: Vendor Name
JavaFX-Class-Path: Kit.jar