docs: private String[] getAttributeGroupInterfaces(XsdElement element){
          List<String> attributeGroups = new ArrayList<>();
          XsdComplexType complexType = element.getXsdComplexType();
          Stream<XsdAttributeGroup> extensionAttributeGroups = Stream.empty();
          XsdExtension extension = getXsdExtension(element);
  
          if (complexType != null){
              if (extension != null){
                  extensionAttributeGroups = extension.getXsdAttributeGroup();
              }
  
              attributeGroups.addAll(getTypeAttributeGroups(complexType, extensionAttributeGroups));
          }
  
          return listToArray(attributeGroups, CUSTOM_ATTRIBUTE_GROUP);
      }