java.lang.IllegalStateException: Attempt to call defer when toolkit not running

java.lang.IllegalStateException: Attempt to call defer when toolkit not running
at com.sun.javafx.tk.quantum.QuantumToolkit.defer(QuantumToolkit.java:725)
at com.sun.javafx.application.PlatformImpl.runLater(PlatformImpl.java:238)
at com.sun.javafx.application.PlatformImpl.runLater(PlatformImpl.java:214)
at javafx.application.Platform.runLater(Platform.java:53)
at javafx.scene.Scene$MouseHandler.pulse(Scene.java:3370)
at javafx.scene.Scene$MouseHandler.access$4100(Scene.java:3326)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2315)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:325)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:533)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:513)
at com.sun.javafx.tk.quantum.QuantumToolkit$16.run(QuantumToolkit.java:380)

(actually I have no steps to reproduce, error occured once in modality tests)