javafx.scene.input.ClipboardContent.putString(String) and other putXXX methods are documented as follows:
- returns true if value was put on clipboard
- value is cleared if null is passed

Both is not consistent with the code:
- code would return false if value was put on clipboard (returns true when putXXX call is made twice ;-)
- null argument throws NPE

Actually, the doc is inconsistent in itself:
- "Setting this value to null effectively clears it from the clipboard."
- "throws java.lang.NullPointerException - if null reference is passed"