-import com.google.common.annotations.Beta;
-import com.google.common.base.Optional;
-import com.google.common.base.Preconditions;
+import static java.util.Objects.requireNonNull;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.ObjectStreamException;
+import java.util.Optional;