Spring @Autowired and Singletons

I have a Spring application that uses various configuration parameters that are persisted in a database. In order to minimize database access cycles, I have created a Singleton class that holds the parameters in a Properties object. There are occasions when the Properties object needs to be refreshed during the running of the application, so to this end I have a load() method and a reload() method. To access the database, I have an @Autowired service object. Simplifying a little:

public class AppConfig {
    private static AppConfig instance = null;
    private Properties appProperties;

    @Autowired ConfiguraitonService configService;

    protected AppConfig() {
        load();
    }

    public static AppConfig getInstance() {
        if (instance == null) {
            instance = new AppConfig();
        }
        return instance;
    }

    public void reload() {
        load();
    }

    private void load() {
        List<Configuration> configList configService.findAll()

        for (Configuration myConfiguration : configList) {
          if (myConfiguration != null && myConfiguration.getAttribute() != null) {
                appProperties.setProperty(myConfiguration.getAttribute(),myConfiguration.getValue());
            }
        }
    }

public String getValue(String key) {
    return appProperties.getProperty(key);
}

In the Spring configuration file, I have:

<bean id="appConfigBean" class="foo.bar.AppConfig"></bean>

Calling 'getValue' against this Singleton generates a null pointer exception. I understand that this is in someway connected to @Autowired and a failure to initialise correctly, although I don't understand why. I guess my question relates to the best approach for resolving this issue.

For others, this is the modified code that worked:

public class AppConfig {
    private static Properties myProperties = new Properties();

    @Autowired
    private ConfigurationService configService;
    private static AppConfig instance = null;

    protected AppConfig() {
    }

    public static AppConfig getInstance() {
        if (instance == null) {
            instance = new AppConfig();
        }
        return instance;
    }

    @PostConstruct
    public void load() {        
        List<Configuration> configList = configService.findAll();

        for (Configuration myConfiguration : configList) {
            if (myConfiguration != null && myConfiguration.getAttribute() != null) {
                myProperties.setProperty(myConfiguration.getAttribute(), myConfiguration.getValue());
            }
        }
    }