### Question:
PreferencesRecentWorkspacesService implements RecentWorkspacesService { @Override public void addWorkspaceLastUsed(File workspace) { requireNotNullArg(workspace, "Null workspace is not allowed"); cache.put(workspace.getAbsolutePath(), Long.toString(Instant.now().toEpochMilli())); LOG.trace("Added recently used workspace {}", workspace.getAbsolutePath()); } PreferencesRecentWorkspacesService(); @Override void addWorkspaceLastUsed(File workspace); @Override List<String> getRecentlyUsedWorkspaces(); @Override void clear(); void flush(); @EventListener void onShutdown(ShutdownEvent event);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void nullWorkspace() { victim.addWorkspaceLastUsed(null); }