Bug 64667.xlsx prevent NPE loading styles table

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1880834 13f79535-47bb-0310-9956-ffa450edef68

src/ooxml/java/org/apache/poi/xssf/model/StylesTable.java

@@ -239,7 +239,7 @@ public class StylesTable extends POIXMLDocumentPart implements Styles {
             if(styleDxfs != null) dxfs.addAll(Arrays.asList(styleDxfs.getDxfArray()));
 
             CTTableStyles ctTableStyles = styleSheet.getTableStyles();
-            if (ctTableStyles != null) {
+            if (ctTableStyles != null && styleDxfs != null) {
                 int idx = 0;
                 for (CTTableStyle style : ctTableStyles.getTableStyleArray()) {
                     tableStyles.put(style.getName(), new XSSFTableStyle(idx, styleDxfs, style, indexedColors));

src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFBugs.java

@@ -3560,4 +3560,12 @@ public final class TestXSSFBugs extends BaseTestBugzillaIssues {
             Assert.assertEquals("", aCell.getStringCellValue());
         }
     }
+
+    @Test
+    public void testBug64667() throws IOException {
+        //test that an NPE isn't thrown on opening
+        try (Workbook wb = XSSFTestDataSamples.openSampleWorkbook("64667.xlsx")) {
+            int activeSheet = wb.getActiveSheetIndex();
+        }
+    }
 }