@Override
    public <T> T callMethod(
            final Object receiver,
            final String methodName,
            final Object singleArg,
            final Class<T> returnType) throws JRubyInvalidRuntimeException {
        return getInitialized().callMethod(receiver, methodName, singleArg, returnType);
    }
Indirects onto JRuby with initializing ScriptingContainer lazily.
embulk-core/src/main/java/org/embulk/jruby/LazyScriptingContainerDelegate.java