public static Manifest getFirstManifest(final String category) {
        final List<String> jarResourceNames = JAR_RESOURCE_NAMES.get(category);
        if (jarResourceNames.isEmpty()) {
            return null;
        }

        final String firstJarResourceName = jarResourceNames.get(0);
        final SelfContainedJarFile selfContainedJarFile = Holder.INSTANCE.get(firstJarResourceName);
        return selfContainedJarFile.getManifest();
    }
Returns the JAR manifest of the first JAR resource in the category.

<p>This is for self-contained plugins. Plugin's main JAR file (e.g. {@code embulk-input-file.jar}) should be
listed first in the {@code Embulk-Plugin-*} (e.g. {@code Embulk-Plugin-embulk-input-file}) attribute of
Embulk executable's top-level manifest.

<pre>{@code Embulk-Plugin-embulk-decoder-gzip: /lib/embulk-decoder-gzip.jar /lib/commons-compress-1.10.jar}</pre>
embulk-core/src/main/java/org/embulk/cli/SelfContainedJarFiles.java