InvocationStatistics has ConcurrentHashMap entrySet problem

public String toString()
{
StringBuffer tmp = new StringBuffer("<InvocationStatistics concurrentCalls='");
tmp.append(concurrentCalls);
tmp.append("' >\n");

HashMap copy = new HashMap(methodStats);
Iterator iter = copy.entrySet().iterator();
while (iter.hasNext())
{
Map.Entry entry = (Map.Entry) iter.next();
TimeStatistic stat = (TimeStatistic) entry.getValue();
tmp.append("<method name='");
tmp.append(entry.getKey());
tmp.append("' count='");
tmp.append(stat.count);

stat could be null