private static void initializeDependencies(final ArrayList<Path> dependencies) {
        synchronized (DEPENDENCIES) {
            if (DEPENDENCIES.isEmpty()) {
                DEPENDENCIES.addAll(dependencies);
            } else {
                throw new LinkageError("Double initialization of hidden dependencies.");
            }
        }
    }
A singleton class loader to load classes of embulk-core's hidden dependency libraries, such as Jackson.

<p>This class loader is introduced only to control the visibility from plugins, not for customizability.
It is intentionally designed to be a singleton.
embulk-core/src/main/java/org/embulk/EmbulkDependencyClassLoader.java