cleanup for r1812470: avoid NPEs from string.isEmpty()

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1812532 13f79535-47bb-0310-9956-ffa450edef68

src/examples/src/org/apache/poi/ss/examples/html/ToHtml.java

@@ -478,7 +478,7 @@ public class ToHtml {
                         CellFormat cf = CellFormat.getInstance(
                                 style.getDataFormatString());
                         CellFormatResult result = cf.apply(cell);
-                        content = result.text;
+                        content = result.text; //never null
                         if (content.isEmpty()) {
                             content = " ";
                         }

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

@@ -169,8 +169,8 @@ public abstract class BaseTestCellComment {
             assertNotNull("Cells in the second column have comments", sheet.getCellComment(new CellAddress(rownum, 1)));
 
             assertEquals("Yegor Kozlov", comment.getAuthor());
-            assertFalse("cells in the second column have not empyy notes",
-                    comment.getString().getString().isEmpty());
+            assertTrue("cells in the second column should have non-empty notes",
+                    !comment.getString().getString().isEmpty());
             assertEquals(rownum, comment.getRow());
             assertEquals(cell.getColumnIndex(), comment.getColumn());
         }