Bug 55668: Try to avoid NullPointerException when chaning cell type and formula leads to null-string by seting the cell to BLANK instead

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1734861 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/hssf/usermodel/HSSFCell.java

@@ -346,12 +346,19 @@ public class HSSFCell implements Cell {
                 }
                 if (setValue) {
                     String str = convertCellValueToString();
+                    if(str == null) {
+                        // bug 55668: don't try to store null-string when formula
+                        // results in empty/null value
+                        setCellType(CELL_TYPE_BLANK, false, row, col, styleIndex);
+                        return;
+                    } else {
                         int sstIndex = _book.getWorkbook().addSSTString(new UnicodeString(str));
                         lrec.setSSTIndex(sstIndex);
                         UnicodeString us = _book.getWorkbook().getSSTString(sstIndex);
                         _stringValue = new HSSFRichTextString();
                         _stringValue.setUnicodeString(us);
                     }
+                }
                 _record = lrec;
                 break;
 
@@ -884,7 +891,7 @@ public class HSSFCell implements Cell {
      * the HSSFWorkbook.</p>
      * 
      * <p>To change the style of a cell without affecting other cells that use the same style,
-     * use {@link org.apache.poi.ss.util.CellUtil#setCellStyleProperties(org.apache.poi.ss.usermodel.Cell, Map)}</p>
+     * use {@link org.apache.poi.ss.util.CellUtil#setCellStyleProperties(org.apache.poi.ss.usermodel.Cell, java.util.Map)}</p>
      *
      * @param style  reference contained in the workbook
      * @see org.apache.poi.hssf.usermodel.HSSFWorkbook#createCellStyle()

src/testcases/org/apache/poi/hssf/usermodel/TestBugs.java

@@ -2977,4 +2977,28 @@ public final class TestBugs extends BaseTestBugzillaIssues {
 
         wb.close();
     }
+
+    @Test
+    public void test55668() throws IOException {
+        Workbook wb = HSSFTestDataSamples.openSampleWorkbook("55668.xls");
+
+        Sheet sheet = wb.getSheetAt(0);
+        Row row = sheet.getRow(0);
+        Cell cell = row.getCell(0);
+        assertEquals(Cell.CELL_TYPE_FORMULA, cell.getCellType());
+        assertEquals("IF(TRUE,\"\",\"\")", cell.getCellFormula());
+        assertEquals("", cell.getStringCellValue());
+        cell.setCellType(Cell.CELL_TYPE_STRING);
+
+        assertEquals(Cell.CELL_TYPE_BLANK, cell.getCellType());
+        try {
+            assertNull(cell.getCellFormula());
+            fail("Should throw an exception here");
+        } catch (IllegalStateException e) {
+            // expected here
+        }
+        assertEquals("", cell.getStringCellValue());
+
+        wb.close();
+    }
 }