About: http://webisa.webdatacommons.org/129705276

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	B is an object, so it is not cast to A. Therefore, when the method tries to add it internally to the underlying data structure, it raises the exception.
http://www.w3.org/ns/prov#wasQuotedFrom	stackoverflow.com