Stack Trace IllegalStateException

Nov 15, 2014 5:41:12 PM com.jme3.app.Application handleError
SEVERE: Uncaught exception thrown in Thread[LWJGL Renderer Thread,5,main]
java.lang.IllegalStateException: No loader registered for type ""
    at com.jme3.asset.ImplHandler.aquireLoader(ImplHandler.java:198)
    at com.jme3.asset.DesktopAssetManager.loadAsset(DesktopAssetManager.java:271)
    at com.jme3.asset.DesktopAssetManager.loadTexture(DesktopAssetManager.java:346)
    at com.jme3.asset.DesktopAssetManager.loadTexture(DesktopAssetManager.java:356)
    at tonegod.gui.core.Element.<init>(Element.java:281)
    at tonegod.gui.controls.buttons.Button.setButtonIcon(Button.java:515)
    at com.navybofus.GUI.createInventorySlot(GUI.java:142)
    at com.navybofus.GUI.createInvSlots(GUI.java:88)
    at com.navybofus.GUI.initInventory(GUI.java:78)
    at com.navybofus.GUI.initCursor(GUI.java:55)
    at com.navybofus.GUI.<init>(GUI.java:49)
    at com.navybofus.Main.simpleInitApp(Main.java:101)
    at com.jme3.app.SimpleApplication.initialize(SimpleApplication.java:226)
    at com.jme3.system.lwjgl.LwjglAbstractDisplay.initInThread(LwjglAbstractDisplay.java:130)
    at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:207)
    at java.lang.Thread.run(Thread.java:744)

BUILD SUCCESSFUL (total time: 5 seconds)