Pass empty lists instead of nulls to FileAccessTree.of (elastic#129942)

Author: prdoyle

libs/entitlement/src/test/java/org/elasticsearch/entitlement/runtime/policy/FileAccessTreeTests.java

@@ -461,7 +461,7 @@ public void testWindowsAbsolutPathAccess() {
                 )
             ),
             TEST_PATH_LOOKUP,
-            null,
+            List.of(),
             List.of()
         );
 
@@ -487,7 +487,7 @@ public void testWindowsMixedCaseAccess() {
                 )
             ),
             TEST_PATH_LOOKUP,
-            null,
+            List.of(),
             List.of()
         );