How to use vertical Divider in material ui (react) between Grid elements?

Question

React

<Paper>
    <Grid container direction="row">
      <Grid item lg={6} direction="column">
        <Grid item>
          <SearchBar />
        </Grid>
        <Grid item>
          <UserList />
        </Grid>
      </Grid>
      <Divider orientation="vertical" />
      <Grid item lg={6}>
        123
      </Grid>
    </Grid>
  </Paper>

Here's a variant of the code, the vertical Divider is not shown, why?