Fix bug #56278 - Support loading .xlsx files with no Styles Table

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1578518 13f79535-47bb-0310-9956-ffa450edef68

src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java

@@ -295,6 +295,11 @@ public class XSSFWorkbook extends POIXMLDocument implements Workbook, Iterable<X
                     shIdMap.put(p.getPackageRelationship().getId(), (XSSFSheet)p);
                 }
             }
+            
+            if (stylesSource == null) {
+                // Create Styles if it is missing
+                stylesSource = (StylesTable)createRelationship(XSSFRelation.STYLES, XSSFFactory.getInstance());
+            }
             stylesSource.setTheme(theme);
 
             if(sharedStringSource == null) {

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

@@ -1440,4 +1440,19 @@ public final class TestXSSFBugs extends BaseTestBugzillaIssues {
         assertEquals("#@_#", c.getStringCellValue()); 
         assertEquals("http://invalid.uri", c.getHyperlink().getAddress()); 
     }
+    
+    /**
+     * Was giving NullPointerException
+     * at org.apache.poi.xssf.usermodel.XSSFWorkbook.onDocumentRead
+     * due to a lack of Styles Table
+     */
+    @Test
+    public void bug56278() throws Exception {
+        Workbook wb = XSSFTestDataSamples.openSampleWorkbook("56278.xlsx");
+        assertEquals(0, wb.getSheetIndex("Market Rates"));
+        
+        // Save and re-check
+        Workbook nwb = XSSFTestDataSamples.writeOutAndReadBack(wb);
+        assertEquals(0, nwb.getSheetIndex("Market Rates"));
+    }
 }