if (config.root().size() != 1) {
throw new ConfigException.Parse(config.root().origin(),
"config root must have exactly one key");
}
String category = config.root().keySet().iterator().next();
PluginMap pluginMap = pluginRegistry.asMap().get(category);
if (pluginMap == null) {
throw new ConfigException.BadValue(config.root().get(category).origin(),
category,
"top level key must be a valid category");
}