From 04f4c1fa7424f12b12f1e513950f9e7fa13c625d Mon Sep 17 00:00:00 2001
From: Dominik Stadler <dominik.stadler@gmx.at>
Date: Fri, 23 Jan 2026 07:13:50 +0100
Subject: [PATCH] Avoid NPE when retrieving sheets by name with invalid name

---
 .../main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java
index a62bbfb739..a063b4d8a9 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java
@@ -1218,6 +1218,10 @@ public class XSSFWorkbook extends POIXMLDocument implements Workbook, Date1904Su
      */
     @Override
     public XSSFSheet getSheet(String name) {
+        if (name == null) {
+            throw new IllegalArgumentException("Encountered an empty name when looking up sheets by name");
+        }
+
         for (XSSFSheet sheet : sheets) {
             if (name.equalsIgnoreCase(sheet.getSheetName())) {
                 return sheet;