public void verifyReadyForDynamicMode(String desiredAction) {
        assert desiredAction != null;

        verifyAddedToSpatial(desiredAction);

        if (!isReady) {
            String message = "Cannot " + desiredAction
                    + " until the physics has been stepped.";
            throw new IllegalStateException(message);
        }
    }
Verify that this control is ready for dynamic mode, which implies that it
is added to a Spatial.

@param desiredAction (not null, not empty)
jme3-jbullet/src/main/java/com/jme3/bullet/animation/DacLinks.java