Annotate Guava Immutable collections

Annotate Guava Immutable collections

The following methods in Immutable{List|Set|Map} are all used
to create new collections and never return null values:

builder()
Builder.build()
copyOf()
of()

They can all be annotated as @NonNull.

Change-Id: I7149f488d2905c5def7b7b39993e9584642a4b0a
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/59326
Reviewed-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>