Hadoop singleton pattern uasge

I'm trying to implement singleton which is going to cache and validate configuration of map reduce jobs in hadoop. Let's name it ConfigurationManager.

Here is what I have for now:

public class ConfigurationManager {
    private static ConfigurationManager instance;
    private static final String CONF_NAME = "isSomethingEnabled";
    private boolean isSomethingEnabled;

    private ConfigurationManager(Configuration configuration) {
        this.isSomethingEnabled= configuration.getBoolean(CONF_NAME, false);
    }

    public static ConfigurationManager get(Configuration configuration) {
        if (instance == null) {
            synchronized (ConfigurationManager.class) {
                if (instance == null) {
                    instance = new ConfigurationManager(configuration);
                }
            }
        }
        return instance;
    }

    public boolean isSomethingEnabled() {
        return isSomethingEnabled;
    }
}  

As you can see it is designed to be thread-safe. Moreover it is not standard singleton: I separated initialization and accessor methods not to enforce presence of hadoop's Configuration instance on get call. So to use it I prematurely call init in the ancestor of Tool and then trying to access my singleton using get in reducers (like this ConfigurationManager.get().isSomethingEnabled()), but for some reasons get returns null. Could somebody, please, explain such a behaviour? Maybe maps/reducers are initiated as separate processes?