我目前使用的NPOI版本為2.5.4
想要在頁首增加圖片
但目前卡在一個奇怪的狀況

XWPFDocument document = new XWPFDocument();
document.Document.body.sectPr = new CT_SectPr();
CT_SectPr ctSectPr = document.Document.body.sectPr;
CT_Hdr hdr = new CT_Hdr();

XWPFRelation relation = XWPFRelation.HEADER;
var header = document.CreateRelationship(relation, XWPFFactory.GetInstance(), document.HeaderList.Count + 1) as XWPFHeader;
header.SetHeaderFooter(hdr);

using (var headerStream = new FileStream(headerImagePath, FileMode.Open, FileAccess.Read)){
    using (var reader = new BinaryReader(headerStream)){
    header.AddPictureData(reader.ReadBytes((int)reader.BaseStream.Length), (int)PictureType.JPEG);
    
    }
}
CT_HdrFtrRef hdrFtrRef = ctSectPr.AddNewHeaderReference();
hdrFtrRef.type = ST_HdrFtr.@default;
hdrFtrRef.id = header.GetPackageRelationship().Id;

其中

header.AddPictureData(reader.ReadBytes((int)reader.BaseStream.Length), (int)PictureType.JPEG);

出現System.NullReferenceException : 並未將物件參考設定為物件的執行個體。的例外狀況，但是有確定輸入都沒有Null的值出現

去看NPOI提供的範例也沒提到怎麼增加頁首圖片
網路查到的也都是舊版的寫法

更新

後來依照海綿寶寶提供的2019年連結照著修改
順利把圖片加上頁首了

下面是修改後的程式碼，稍微紀錄一下

XWPFDocument document = new XWPFDocument();

//XWPFParagraph paragraph = document.CreateParagraph();
//XWPFRun run = paragraph.CreateRun();

XWPFHeader header = document.CreateHeaderFooterPolicy().CreateHeader(ST_HdrFtr.@default);
            var paragraph = header.GetParagraphArray(0);
            paragraph.Alignment = ParagraphAlignment.CENTER;
            var run = paragraph.CreateRun();
            
using (var headerStream = new FileStream(headerImagePath, FileMode.Open, FileAccess.Read)){
                run.AddPicture(headerStream, (int)PictureType.JPEG, fileName, Units.ToEMU(headerW * cmCoefficient), Units.ToEMU(headerH * cmCoefficient));
}