Open article.module

Starting at line 153 you should see the following:

    if ($term) {
      $output = theme('box', t('%term_name - Sub Categories',
			       array('%term_name' => $term->name)),
		      article_index($term->tid));
      $output .= taxonomy_render_nodes(taxonomy_select_nodes(array($term->tid), 'or', variable_get('article_index_depth', 'all')));
      return $output;
    }
    else {
      drupal_set_message(t('The category you requested can not be found.'));
      return '';
    }

Replace the above code with this:

    if ($term) {
      $output1 = theme('box', t('%term_name - Sub Categories',
			       array('%term_name' => $term->name)),
		      article_index($term->tid));
	  if(article_index($term->tid) != NULL){
	  	$output = $output1;
	  }else{
	  	$output = "";
	  }
      $output .= taxonomy_render_nodes(taxonomy_select_nodes(array($term->tid), 'or', variable_get('article_index_depth', 'all')));
      return $output;
    }
    else {
      drupal_set_message(t('The category you requested can not be found.'));
      return '';
    }
	
Enjoy!
Jason T