fixes #2136 - NPE in ExpressionOperator.printCollection (#2137)

* fixes #2136 NPE in NullPointerException in ExpressionOperator.printCollection since 2.7.11
The bug is described in detail in #2136
We are looping over an array which is located in the instance field which can be set to `null` while lopping which is causing NPE.
To fix it we are caching the value of `argumentIndices` by looping over an iterator of the array.

foundation/org.eclipse.persistence.core/src/org/eclipse/persistence/expressions/ExpressionOperator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2023 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2024 Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2018, 2022 IBM Corporation. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
@@ -2388,8 +2388,7 @@ public void printCollection(List<Expression> items, ExpressionSQLPrinter printer
         }
 
         String[] dbStrings = getDatabaseStrings(items.size());
-        for (int i = 0; i < this.argumentIndices.length; i++) {
-            final int index = this.argumentIndices[i];
+        for (final int index : this.argumentIndices) {
             Expression item = items.get(index);
             if ((this.selector == Ref) || ((this.selector == Deref) && (item.isObjectExpression()))) {
                 DatabaseTable alias = ((ObjectExpression)item).aliasForTable(((ObjectExpression)item).getDescriptor().getTables().firstElement());