Take defaults into account even though they aren't used yet

Makes code like SortedProperties

Author: garydgregory

src/main/java/org/apache/commons/collections4/properties/OrderedProperties.java

@@ -129,7 +129,7 @@ public synchronized Object merge(final Object key, final Object value,
 
     @Override
     public Enumeration<?> propertyNames() {
-        return Collections.enumeration(orderedKeys);
+        return Collections.enumeration(stringPropertyNames());
     }
 
     @Override