private Path getLocalMavenRepository() throws PluginSourceNotMatchException {
        // It expects the Embulk system property "m2_repo" is set from org.embulk.cli.EmbulkSystemPropertiesBuilder.
        final String m2Repo = this.embulkSystemProperties.getProperty("m2_repo", null);
        if (m2Repo == null) {
            throw new PluginSourceNotMatchException("Embulk system property \"m2_repo\" is not set properly.");
        }

        return Paths.get(m2Repo);
    }
Caches Maven-based plugin's loaded classes such as embulk-ruby's Embulk::PluginRegistry.

<p>See {@code /embulk-ruby/lib/embulk/plugin_registry.rb}.
embulk-core/src/main/java/org/embulk/plugin/maven/MavenPluginRegistry.java