Merge pull request #1885 from SmireG/bugfix1765

fix #1765

src/main/java/com/alibaba/excel/write/property/ExcelWriteHeadProperty.java

@@ -142,7 +142,7 @@ public class ExcelWriteHeadProperty extends ExcelHeadProperty {
                     continue;
                 }
                 alreadyRangeSet.add(i + "-" + j);
-                String headName = headNameList.get(j);
+                String headName = headNameList.get(j) == null ? "" : headNameList.get(j);
                 int lastCol = i;
                 int lastRow = j;
                 for (int k = i + 1; k < headList.size(); k++) {

src/test/java/com/alibaba/easyexcel/test/demo/Test1765/Issue1765.java

@@ -0,0 +1,55 @@
+package com.alibaba.easyexcel.test.demo.Test1765;
+
+import com.alibaba.easyexcel.test.util.TestFileUtil;
+import com.alibaba.excel.EasyExcel;
+import com.alibaba.excel.EasyExcelFactory;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.List;
+
+public class Issue1765 {
+    @Test
+    public void test1765() throws FileNotFoundException {
+        String fileName = "src/test/java/com/alibaba/easyexcel/test/demo/Test1765/Data1765.xlsx";
+        EasyExcel.write(fileName).head(head()).sheet("模板").doWrite(dataList());
+    }
+
+
+    private List<List<String>> head() {
+        List<List<String>> list = new ArrayList<List<String>>();
+        List<String> head0 = new ArrayList<String>();
+        List<String> head1 = new ArrayList<String>();
+        List<String> head2 = new ArrayList<String>();
+        List<String> head3 = new ArrayList<String>();
+        head0.add("表头");
+        head1.add("日期");
+        head2.add(null);
+        head3.add("数字");
+        list.add(head0);
+        list.add(head1);
+        list.add(head2);
+        list.add(head3);
+
+        return list;
+    }
+
+    private List<List<Object>> dataList() {
+        List<List<Object>> list = new ArrayList<List<Object>>();
+        for (int i = 0; i < 5; i++) {
+            List<Object> data = new ArrayList<Object>();
+            data.add("字符串" + i);
+            data.add(new Date());
+            data.add(i * 2);
+            data.add(i * 3);
+            list.add(data);
+        }
+        return list;
+    }
+}