[bug-64044] setCellValue(LocalDate) does not support nulls properly

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1872246 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/ss/usermodel/Cell.java

@@ -210,7 +210,7 @@ public interface Cell {
      *        will change the cell to a numerics cell and set its value.
      */
     default void setCellValue(LocalDate value) {
-        setCellValue(value.atStartOfDay());
+        setCellValue(value == null ? null : value.atStartOfDay());
     }
 
     /**

src/testcases/org/apache/poi/ss/usermodel/BaseTestCell.java

@@ -133,6 +133,21 @@ public abstract class BaseTestCell {
             assertProhibitedValueAccess(cell, CellType.BOOLEAN, CellType.STRING,
                                         CellType.FORMULA, CellType.ERROR);
 
+            String strNull = null;
+            cell.setCellValue(strNull);
+            assertNull(cell.getRichStringCellValue());
+            assertEquals(CellType.BLANK, cell.getCellType());
+
+            LocalDate ldNull = null;
+            cell.setCellValue(ldNull);
+            assertNull(cell.getLocalDateTimeCellValue());
+            assertEquals(CellType.BLANK, cell.getCellType());
+
+            LocalDateTime ldtNull = null;
+            cell.setCellValue(ldtNull);
+            assertNull(cell.getLocalDateTimeCellValue());
+            assertEquals(CellType.BLANK, cell.getCellType());
+
             cell.setCellErrorValue(FormulaError.NA.getCode());
             assertEquals(FormulaError.NA.getCode(), cell.getErrorCellValue());
             assertEquals(CellType.ERROR, cell.getCellType());