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快速开始 、 常见问题
触发场景描述
当class head 和list head大小不一致时，ExcelWriteHeadProperty构造函数会报空指针错误
触发Bug的代码

1.    public ExcelWriteHeadProperty(Holder holder, Class<?> headClazz, List<List<String>> head) {
2.         super(holder, headClazz, head);
3.         if (getHeadKind() != HeadKindEnum.CLASS) {
4.             return;
5.         }
6.         this.headRowHeightProperty =
7.             RowHeightProperty.build(headClazz.getAnnotation(HeadRowHeight.class));
8.         this.contentRowHeightProperty =
9.             RowHeightProperty.build(headClazz.getAnnotation(ContentRowHeight.class));
10.         this.onceAbsoluteMergeProperty =
11.             OnceAbsoluteMergeProperty.build(headClazz.getAnnotation(OnceAbsoluteMerge.class));
12. 
13.         ColumnWidth parentColumnWidth = headClazz.getAnnotation(ColumnWidth.class);
14.         HeadStyle parentHeadStyle = headClazz.getAnnotation(HeadStyle.class);
15.         HeadFontStyle parentHeadFontStyle = headClazz.getAnnotation(HeadFontStyle.class);
16. 
17. 
18.         for (Map.Entry<Integer, Head> entry : getHeadMap().entrySet()) {
19.             Head headData = entry.getValue();
20.             if (headData == null) {
21.                 throw new IllegalArgumentException(
22.                     "Passing in the class and list the head, the two must be the same size.");
23.             }
24.             Field field = headData.getField();
25.             if (field != null) {
26.                 ColumnWidth columnWidth = field.getAnnotation(ColumnWidth.class);
27.                 if (columnWidth == null) {
28.                     columnWidth = parentColumnWidth;
29.                 }
30.                 headData.setColumnWidthProperty(ColumnWidthProperty.build(columnWidth));
31. 
32. 
33.                 HeadStyle headStyle = field.getAnnotation(HeadStyle.class);
34.                 if (headStyle == null) {
35.                     headStyle = parentHeadStyle;
36.                 }
37.                 headData.setHeadStyleProperty(StyleProperty.build(headStyle));
38. 
39.                 HeadFontStyle headFontStyle = field.getAnnotation(HeadFontStyle.class);
40.                 if (headFontStyle == null) {
41.                     headFontStyle = parentHeadFontStyle;
42.                 }
43.                 headData.setHeadFontProperty(FontProperty.build(headFontStyle));
44. 
45.                 headData.setLoopMergeProperty(LoopMergeProperty.build(field.getAnnotation(ContentLoopMerge.class)));
46.             } else {
47.                 headData.setColumnWidthProperty(ColumnWidthProperty.build(null));
48.                 headData.setHeadStyleProperty(StyleProperty.build((HeadStyle) null));
49.                 headData.setHeadFontProperty(FontProperty.build((ContentFontStyle) null));
50.                 headData.setLoopMergeProperty(LoopMergeProperty.build(null));
51.             }
52.         }
53.     }

提示的异常或者没有达到的效果
当class head 和list head大小不一致时，实际第20行headData并不为null（有headNameList但是没有field），不会触发IllegalArgumentException，会在第24行触发NPE，这里不明白为什么需要限制两者size一致。

我有个需求是希望头有4列，但是写入的数据只需要写前3列，而且希望按照实体类的方式写出（参考variableTitleWrite()的方式），上面代码加了一个if else判断可以成功写出，不知道两者不一致会有什么隐患。