Two selectInputDates with same id cause NullPointerException

ICEFaces 1.8.2 throws a NullPointerException. The stack trace shows that the exception is thrown by:

com.icesoft.faces.component.selectinputdate.SelectInputDateRenderer.encodeEnd(SelectInputDateRenderer.java:541)

In my case it turns out that this exception was caused by two SelectInputDate instances with the same id. Unfortunately, ICEFaces does not give a concise error message.