AbstractAddStepHandler is capable of detecting registered attributes automatically and its AbstractAddStepHandler.attributes class field was deprecated, see WFCORE-6407.

However, the org.wildfly.extension.undertow.ServerAdd was not fixed accordingly and it is still incorrectly getting the attributes using AbstractAddStepHandler.attributes class field.

Although AbstractAddStepHandler.attributes, its usage should be removed completely when it is not initialized with a deprecated constructor, otherwise this class field will not be initialized to the expected attribute list.