Mucha
https://docs.oracle.com/javase/7/doc...til.Collection)
Cita: ArrayList
public ArrayList(Collection<? extends E> c)
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
Parameters:
c - the collection whose elements are to be placed into this list
Throws:
NullPointerException - if the specified collection is null
En la primera usas un list(tftp.generarPaquetes) para crear otro list, si es null te dará nullpointerexception.
En la segunda asignas un list(tftp.generarPaquetes) a una referencia, da igual si es o no null.