manual review 2.3.5 - 1

• /null_pointer_1.java
• /null_pointer_2.java
• /null_pointer_3.java

Summary by Bito

This pull request enhances the InventoryManagementSystem by implementing null safety checks across three files to prevent NullPointerExceptions. The changes focus on securing collection processing, including iterations, streams, and nested data structures. These modifications strengthen error handling for inventory, supplier, and order functionalities, improving overall system stability and reliability.