Clean Guava way to handle possibly-null collection

Question

I have a method which takes an argument Collection foos, which could be NULL. I want to end up with a local copy of the input as an ImmutableS

Answer 1

I don't see why you couldn't use Objects.firstNonNull:

this.foos = ImmutableSet.copyOf(Objects.firstNonNull(foos, ImmutableSet.of()));

You can save some typing with static imports, if that's your thing:

import static com.google.common.collect.ImmutableSet.copyOf;
import static com.google.common.collect.ImmutableSet.of;
// snip...
this.foos = copyOf(Objects.firstNonNull(foos, of()));

Answer 2

A Collection is a reference like any other, so you could do:

ImmutableSet.copyOf(Optional.fromNullable(foos).or(ImmutableSet.of()));

But that is becoming quite a handful to write. More simple:

foos == null ? ImmutableSet.of() : ImmutableSet.copyOf(foos);