code: void addRelationshipAttributeType(String attributeName, AtlasRelationshipType relationshipType) {
          List<AtlasRelationshipType> relationshipTypes = relationshipAttributesType.get(attributeName);
  
          if (relationshipTypes == null) {
              relationshipTypes = new ArrayList<>();
              relationshipAttributesType.put(attributeName, relationshipTypes);
          }
  
          relationshipTypes.add(relationshipType);
      }
docs: this method should be called from AtlasRelationshipType.resolveReferencesPhase2()