public Enumeration keys() {
if (defaults == null)
return new ContextKeyToStringEnum(properties.keys());
Enumeration allKeys = new MergedEnumeration(new ContextKeyToStringEnum(properties.keys()), defaults.keys());
Hashtable keysSet = new Hashtable();
while (allKeys.hasMoreElements())
keysSet.put(allKeys.nextElement(), "ignored"); //$NON-NLS-1$
return keysSet.keys();
}