public static void init() {
        try {
            ConfigFileLoader.getSource(); // throws IllegalStateException if source is not set.
        } catch (Exception e) {
            // Set only when a user did not set the source.
            ConfigFileLoader.setSource(new ConfigurationSource() {
                @Override
                public Resource getResource(String name) throws IOException {
                    throw new FileNotFoundException(name);
                }

                @Override
                public URI getURI(String name) {
                    throw new UnsupportedOperationException();
                }
            });
        }
    }
Sets the dummy {@link ConfigurationSource} so that {@link ContextConfig} does not complain.
tomcat10/src/main/java/com/linecorp/armeria/internal/server/tomcat/ConfigFileLoaderInitializer.java