@Override
public void sync(final DataContainer first, final DataContainer second)
throws DataContainerException {
if (first.value == null) first.value = second.value;
else if (second.value == null) second.value = first.value;
else if (!first.value.equals(second.value)) throw new OverrideValue();
} /* sync */
@Override
public void sync(final DataContainer first, final DataContainer second)
throws DataContainerException {
if (first.help == null) first.help = second.help;
else if (second.help == null) second.help = first.help;
else if (!first.help.equals(second.help)) throw new OverrideHelp();
} /* sync */