Bug 66425: Avoid a NullPointerException found via oss-fuzz

We try to avoid throwing NullPointerException, but it was possible
to trigger one here with a specially crafted input-file

Should fix https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=62059

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1912127 13f79535-47bb-0310-9956-ffa450edef68

poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFTableStyle.java

@@ -84,6 +84,9 @@ public class XSSFTableStyle implements TableStyle {
         }
 
         for (CTTableStyleElement element : tableStyle.getTableStyleElementList()) {
+            if (element.getType() == null) {
+                throw new IllegalArgumentException("Did not have a type in table-style " + element);
+            }
             TableStyleType type = TableStyleType.valueOf(element.getType().toString());
             DifferentialStyleProvider dstyle = null;
             if (element.isSetDxfId()) {