Here's the backtrace for the error:
[X1QH3BjFAzimaGlZi2m3AQABBAg] /wiki/index.php/Special:RDFImport Error from line 729 of /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_Store.php: Call to a member function escape() on null
Backtrace:
#0 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreQueryHandler.php(31): ARC2_Store->getTermID(string, string)
#1 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(1023): ARC2_StoreQueryHandler->getTermID(string, string)
#2 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(996): ARC2_StoreSelectQueryHandler->getTriplePatternSQL(array, string)
#3 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(1005): ARC2_StoreSelectQueryHandler->getPatternSQL(array, string)
#4 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(996): ARC2_StoreSelectQueryHandler->getDefaultPatternSQL(array, string)
#5 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(1005): ARC2_StoreSelectQueryHandler->getPatternSQL(array, string)
#6 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(996): ARC2_StoreSelectQueryHandler->getDefaultPatternSQL(array, string)
#7 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(924): ARC2_StoreSelectQueryHandler->getPatternSQL(array, string)
#8 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(475): ARC2_StoreSelectQueryHandler->getWHERESQL()
#9 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(68): ARC2_StoreSelectQueryHandler->getQuerySQL()
#10 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_StoreSelectQueryHandler.php(36): ARC2_StoreSelectQueryHandler->getSQL()
#11 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_Store.php(648): ARC2_StoreSelectQueryHandler->runQuery(array, integer)
#12 /home/bookbin1/public_html/wiki/vendor/semsol/arc2/store/ARC2_Store.php(598): ARC2_Store->runQuery(array, string, integer, string)
#13 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/RDFIO_ARC2StoreWrapper.php(138): ARC2_Store->query(string)
#14 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/RDFIO_ARC2StoreWrapper.php(162): RDFIOARC2StoreWrapper->getURIForEquivURI(string, boolean)
#15 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/parsers/RDFIO_URIToWikiTitleConverter.php(68): RDFIOARC2StoreWrapper->getWikiTitleByEquivalentURI(string)
#16 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/parsers/RDFIO_URIToWikiTitleConverter.php(51): RDFIOURIToTitleConverter->getExistingTitleForURI(string)
#17 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/parsers/RDFIO_ARC2ToWikiConverter.php(31): RDFIOURIToTitleConverter->convert(string)
#18 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/RDFIO_RDFImporter.php(77): RDFIOARC2ToWikiConverter->convert(array, array, array)
#19 /home/bookbin1/public_html/wiki/extensions/Rdfio/classes/RDFIO_RDFImporter.php(48): RDFIORDFImporter->importFromArc2Data(array, array, array)
#20 /home/bookbin1/public_html/wiki/extensions/Rdfio/specials/SpecialRDFImport.php(87): RDFIORDFImporter->importTurtle(string)
#21 /home/bookbin1/public_html/wiki/extensions/Rdfio/specials/SpecialRDFImport.php(35): RDFImport->importData(RDFIORequestData)
#22 /home/bookbin1/public_html/wiki/includes/specialpage/SpecialPage.php(575): RDFImport->execute(NULL)
#23 /home/bookbin1/public_html/wiki/includes/specialpage/SpecialPageFactory.php(611): SpecialPage->run(NULL)
#24 /home/bookbin1/public_html/wiki/includes/MediaWiki.php(296): MediaWiki\Special\SpecialPageFactory->executePath(Title, RequestContext)
#25 /home/bookbin1/public_html/wiki/includes/MediaWiki.php(900): MediaWiki->performRequest()
#26 /home/bookbin1/public_html/wiki/includes/MediaWiki.php(527): MediaWiki->main()
#27 /home/bookbin1/public_html/wiki/index.php(44): MediaWiki->run()
#28 {main}
-Suzy