Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: JohnBergant

src/main/java/org/primeframework/mvc/parameter/el/Accessor.java

@@ -281,7 +281,16 @@ protected void setValueIntoCollection(int index, Object value) {
   }
 
   private int validateIndex(Object key, int maximumLength) {
-    int index = Integer.parseInt(key.toString());
+    if (key == null) {
+      throw new IndexExpressionException("Encountered an indexed property without an index");
+    }
+
+    final int index;
+    try {
+      index = Integer.parseInt(key.toString());
+    } catch (NumberFormatException e) {
+      throw new IndexExpressionException("Encountered a non-numeric index [" + key + "]", e);
+    }
 
     if (index < 0) {
       throw new InvalidCollectionSizeException(index);