BlockingControlLink compare method fails to handle null block or untilFinished

BlockingControlLink allows both block and untilFinished to be null.

methond compareTo(Object o) calls copare(Object o) without first checking if they are null
This causes a null pointer exception.

Fix:
public int compareTo(Object o) {
if (!(o instanceof BlockingControlLink))

{ return o.getClass().getCanonicalName().compareTo(getClass().getCanonicalName()); }

BlockingControlLink o1 = this;
BlockingControlLink o2 = (BlockingControlLink) o;

if ( o1.getUntilFinished() == null){
if (o2.getUntilFinished() == null)

{ return 1; }
} else {
int untilFinished = o1.getUntilFinished().compareTo(o2.getUntilFinished());
if (untilFinished != 0) { return untilFinished; }
}

if (o1.getBlock() == null) {
if (o2.getBlock() == null){ return 0; } else { return 1; }

}
int block = o1.getBlock().compareTo(o2.getBlock());
return block;
}