code: public List<String> getCategories(){
  		List<String> categories = FieldUtil.getCategories(getField());
  
  		if(categories != null && !categories.isEmpty()){
  			return categories;
  		}
  
  		return null;
  	}
docs: <p>
  Returns the range of categories for this categorical or ordinal field.
  </p>
  
  @return A non-empty list, or <code>null</code>.
  
  @see #getOpType()
  
  @see CategoricalResultFeature
  @see CategoricalResultFeature#getCategories()