test date parse for NaN
test date parse for NaN

retorquere/zotero-better-bibtex,ZotPlus/zotero-better-bibtex,retorquere/zotero-better-bibtex,ZotPlus/zotero-better-bibtex,ZotPlus/zotero-better-bibtex,retorquere/zotero-better-bibtex,retorquere/zotero-better-bibtex,retorquere/zotero-better-bibtex,retorquere/zotero-better-bibtex,ZotPlus/zotero-better-bibtex