import org.jetbrains.annotations.NotNull; interface MakeNonNull { @NotNull String getSnapshot(@NotNull Integer arg); } class MakeNonNullImpl implements MakeNonNull { @NotNull @Override public String getSnapshot(Integer arg) { return arg.toString(); } } class MakeNonNullImpl2 implements MakeNonNull { @NotNull @Override public String getSnapshot(Integer arg) { return "1"; } }