FULL PRODUCT VERSION :


A DESCRIPTION OF THE PROBLEM :
You cannot add null to checked collections using add() (and set()) methods. However, nulls can be added through addAll() methods.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compile and execute attached source code

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
[]

l.add(null);
java.lang.ClassCastException

l.addAll(Collections.<String>singletonList(null));
java.lang.ClassCastException

ACTUAL -
[]

l.add(null);
java.lang.NullPointerException
at java.util.Collections$CheckedCollection.typeCheck(Collections.java:2205)
at java.util.Collections$CheckedCollection.add(Collections.java:2246)
at Main.main(Main.java:9)

l.addAll(Collections.<String>singletonList(null));
[null]


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.*;

public class Main {
public static void main(String[] args) {
List<String> l = Collections.checkedList(new ArrayList<String>(), String.class);
System.out.println(l);
try {
System.out.println("\nl.add(null);");
l.add(null);
System.out.println(l);
}
catch(RuntimeException exc) { // <-- goes here
exc.printStackTrace(System.out);
}
try {
System.out.println("\nl.addAll(Collections.<String>singletonList(null));");
l.addAll(Collections.<String>singletonList(null));
System.out.println(l); // <-- goes here
}
catch(RuntimeException exc) {
exc.printStackTrace(System.out);
}
}
}

---------- END SOURCE ----------