public synchronized PluginMetadata getMetadata( String canonicalName )
    {
        return this.pluginMetadata.get( canonicalName );
    }
Returns metadata for an extracted plugin, or null when the plugin is extracted nor loaded.

Note that an <em>installed</em> plugin is not per definition an <em>extracted</em> plugin, and an extracted
plugin is not per definition a <em>loaded</em> plugin.  A plugin that's extracted might, for instance, fail to
load, due to restrictions imposed by its {@code minServerVersion} definition.

@param canonicalName the canonical name (lower case JAR/WAR file without exception) of the plugin
@return A collection of metadata (possibly empty, never null).
xmppserver/src/main/java/org/jivesoftware/openfire/container/PluginManager.java