RDFParseException: the prefix "pw" is not bound

ERROR org.apache.any23.extractor.rdf.BaseRDFExtractor - Error while parsing RDF document.
org.eclipse.rdf4j.rio.RDFParseException: org.xml.sax.SAXParseException; lineNumber: 165; columnNumber: 101; The prefix "pw" for attribute "pw:twitter-via" associated with an element type "div" is not bound.
	at org.semarglproject.rdf4j.rdf.rdfa.RDF4JRDFaParser.parse(RDF4JRDFaParser.java:111)
	at org.semarglproject.rdf4j.rdf.rdfa.RDF4JRDFaParser.parse(RDF4JRDFaParser.java:95)
	at org.apache.any23.extractor.rdf.BaseRDFExtractor.run(BaseRDFExtractor.java:158)
	at org.apache.any23.extractor.rdf.BaseRDFExtractor.run(BaseRDFExtractor.java:57)
	at org.apache.any23.extractor.SingleDocumentExtraction.runExtractor(SingleDocumentExtraction.java:471)
	at org.apache.any23.extractor.SingleDocumentExtraction.run(SingleDocumentExtraction.java:259)
	at org.apache.any23.Any23.extract(Any23.java:302)
	at org.apache.any23.Any23.extract(Any23.java:437)
	at com.utownapp.crawl.tripledb.Triples.lambda$extractTriples$0(Triples.java:146)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.semarglproject.rdf.ParseException: org.xml.sax.SAXParseException; lineNumber: 165; columnNumber: 101; The prefix "pw" for attribute "pw:twitter-via" associated with an element type "div" is not bound.
	at org.semarglproject.rdf.rdfa.RdfaParser.processException(RdfaParser.java:1141)
	at org.semarglproject.source.XmlSource.process(XmlSource.java:50)
	at org.semarglproject.source.StreamProcessor.processInternal(StreamProcessor.java:87)
	at org.semarglproject.source.BaseStreamProcessor.process(BaseStreamProcessor.java:167)
	at org.semarglproject.source.BaseStreamProcessor.process(BaseStreamProcessor.java:154)
	at org.semarglproject.rdf4j.rdf.rdfa.RDF4JRDFaParser.parse(RDF4JRDFaParser.java:109)
	... 12 more
Caused by: org.xml.sax.SAXParseException; lineNumber: 165; columnNumber: 101; The prefix "pw" for attribute "pw:twitter-via" associated with an element type "div" is not bound.
	at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
	at org.semarglproject.source.XmlSource.process(XmlSource.java:48)
	... 16 more