public void writeExternalizableCollection(DataOutput out, Collection<? extends Externalizable> value) throws IOException {
        strategy.writeExternalizableCollection(out, value);
    }
Writes a collection of Externalizable objects. The collection passed as a parameter
must be a collection and not a {@code null} value.

@param out   the output stream.
@param value the collection of Externalizable objects. This value must not be null.
@throws IOException if an error occurs.
xmppserver/src/main/java/org/jivesoftware/util/cache/ExternalizableUtil.java