Easy way to convert Iterable to Collection

Question

In my application I use 3rd party library (Spring Data for MongoDB to be exact).

Methods of this library return Iterable, while the rest of my

Answer 1

I use my custom utility to cast an existing Collection if available.

Main:

public static  Collection toCollection(Iterable iterable) {
    if (iterable instanceof Collection) {
        return (Collection) iterable;
    } else {
        return Lists.newArrayList(iterable);
    }
}

Ideally the above would use ImmutableList, but ImmutableCollection does not allow nulls which may provide undesirable results.

Tests:

@Test
public void testToCollectionAlreadyCollection() {
    ArrayList list = Lists.newArrayList(FIRST, MIDDLE, LAST);
    assertSame("no need to change, just cast", list, toCollection(list));
}

@Test
public void testIterableToCollection() {
    final ArrayList expected = Lists.newArrayList(FIRST, null, MIDDLE, LAST);

    Collection collection = toCollection(new Iterable() {
        @Override
        public Iterator iterator() {
            return expected.iterator();
        }
    });
    assertNotSame("a new list must have been created", expected, collection);
    assertTrue(expected + " != " + collection, CollectionUtils.isEqualCollection(expected, collection));
}

I implement similar utilities for all subtypes of Collections (Set,List,etc). I'd think these would already be part of Guava, but I haven't found it.