Method getUnknownNodes is implemented in AbstractBuilder and should return list of added UnknownSchemaNodeBuilders. The TypeDefinitionBuilderImpl extends AbstractTypeAwareBuilder which extends AbstractBuilder.

In TypeDefinitionBuilderImpl there is override of getUnknownNodes method which returns Collections.emptyList(). If this is intentional it should be at least commented since it brings confusion into code. If it is not intentional the override method should be removed from TypeDefinitionBuilderImpl.

There is no possibility to copy of TypedefinitionBuilders UnknownNodes in CopyUtils.java for copy TypDefinitionBuilder since the getUnknownNodes will always be an empty list.