-import static com.google.common.base.Preconditions.checkState;
-import static java.lang.String.format;
-
+import com.google.common.base.Optional;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Multimap;