fix unused imports reported by errorprone [RemoveUnusedImports]
use Remi's rule: use a method reference if you can and a lambda otherwise
elide parens in unary lambdas
This form allows you to request diffs between any two revisions of this file. For each of the two "sides" of the diff, select a symbolic revision name using the selection box, or choose 'Use Text Field' and enter a numeric revision.