dragboard gesture is null

[kerner1000]

• Uncaught exception on thread Thread[JavaFX Application Thread,5,main]java.lang.NullPointerException: Cannot read field "dragboard" because "this.this$0.dndGesture" is null
  at javafx.scene.Scene$DropTargetListener.drop(Scene.java:3001)
  at com.sun.javafx.tk.quantum.GlassSceneDnDEventHandler.lambda$handleDragDrop$2(GlassSceneDnDEventHandler.java:111)
  at java.base/java.security.AccessController.doPrivileged(Unknown Source)
  at com.sun.javafx.tk.quantum.GlassSceneDnDEventHandler.handleDragDrop(GlassSceneDnDEventHandler.java:107)
  at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleDragDrop$11(GlassViewEventHandler.java:772)
  at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
  at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleDragDrop(GlassViewEventHandler.java:771)
  at com.sun.glass.ui.View.handleDragDrop(View.java:708)
  at com.sun.glass.ui.View.notifyDragDrop(View.java:1037)
  at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
  at com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$11(GtkApplication.java:316)
  at java.base/java.lang.Thread.run(Unknown Source)