code: @Override
  	public void initialize(IAggregator aggregator, IAggregatorExtension extension,
  			IExtensionRegistrar registrar) {
  
  		final String sourceMethod = "initialize"; //$NON-NLS-1$
  		boolean isTraceLogging = log.isLoggable(Level.FINER);
  		if (isTraceLogging) {
  			log.entering(BundleVersionsHash.class.getName(), sourceMethod, new Object[]{aggregator, extension, registrar});
  		}
  		// get the name of the function from the extension attributes
  		propName = extension.getInitParams().getValue("propName"); //$NON-NLS-1$
  		if (propName == null) {
  			propName = DEFAULT_PROPNAME;
  		}
  		if (isTraceLogging) {
  			log.finer("propName = " + propName); //$NON-NLS-1$
  		}
  		if (aggregator instanceof AggregatorImpl) {		// can be an IAggregator mock when unit testing
  			setContributingBundle(((AggregatorImpl)aggregator).getContributingBundle());
  		}
  
  		if (isTraceLogging) {
  			log.exiting(BundleVersionsHash.class.getName(), sourceMethod);
  		}
  	}
docs: /* (non-Javadoc)
  @see com.ibm.jaggr.core.IExtensionInitializer#initialize(com.ibm.jaggr.core.IAggregator, com.ibm.jaggr.core.IAggregatorExtension, com.ibm.jaggr.core.IExtensionInitializer.IExtensionRegistrar)