#vulnerable code 
                                public boolean isInStruct()
    {
        return !containers.isEmpty() && currentContainer().type == ContainerType.STRUCT;
    } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public boolean isInStruct()
    {
        return currentContainerIndex >= 0 && currentContainer().type == ContainerType.STRUCT;
    }