title: How to know if a JCalendar is empty?
body: <p>I have a simple Java program with a <strong>JCalendar</strong>.
  I need to know if my JCalendar <code>calendario</code> is or not empty, it means if the user selected or not a date. I was thinking about a method like <code>calendario.isEmpty</code> but it doesn't exist. Maybe I can compare <code>calendario</code> with <code>null</code> but it didn't work.
  I am using <code>com.toedter.calendar.JDateChooser</code>. </p>