RuntimeException in HelloTreeView

Here's the stack trace:

Exception in Application start method
Exception in thread "main" java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:534)
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:47)
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:133)
    at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.ClassCastException: sun.awt.image.ToolkitImage cannot be cast to java.awt.image.BufferedImage
    at helloworld.HelloTreeView.createNode(HelloTreeView.java:468)
    at helloworld.HelloTreeView.buildFileSystemTab(HelloTreeView.java:452)
    at helloworld.HelloTreeView.start(HelloTreeView.java:193)
    at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:477)