code: private ExtendedAttributeDefinition getAttributeDefinition(RegistryEntry registryEntry, String attributeName) {
          if (registryEntry == null) {
              return null;
          }
  
          ExtendedObjectClassDefinition definition = registryEntry.getObjectClassDefinition();
          if (definition == null) {
              return null;
          }
  
          Map<String, ExtendedAttributeDefinition> attributeMap = definition.getAttributeMap();
          ExtendedAttributeDefinition attributeDefinition = attributeMap.get(attributeName);
          return attributeDefinition;
      }
docs: Answer the definition of an attribute. Answer null if a definition
  is not available.
  
  @param registryEntry The registry entry from which to retrieve the attribute definition.
  @param attributeName The name of the attribute to locate.
  
  @return The definition of the attribute. Null if no definition is available for the attribute.