assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
  }

  @Test
  public void addEdge_parallelSelfLoopEdge_notAllowed() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsSelfLoops()).isTrue();
    assume().that(network.allowsParallelEdges()).isFalse();

    addEdge(N1, N1, E11);
    IllegalArgumentException e =
        assertThrows(

    assume().that(graphIsMutable()).isTrue();
    assume().that(graph.allowsSelfLoops()).isFalse();

    IllegalArgumentException e =
        assertThrows(IllegalArgumentException.class, () -> putEdge(N1, N1));
    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  @Test
  public void putEdge_allowsSelfLoops() {
    assume().that(graphIsMutable()).isTrue();

    assume().that(graphIsMutable()).isTrue();
    assume().that(graph.allowsSelfLoops()).isFalse();

    IllegalArgumentException e =
        assertThrows(IllegalArgumentException.class, () -> putEdge(N1, N1));
    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  @Test
  public void putEdge_allowsSelfLoops() {
    assume().that(graphIsMutable()).isTrue();

    assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
  }

  @Test
  public void addEdge_parallelSelfLoopEdge_notAllowed() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsSelfLoops()).isTrue();
    assume().that(network.allowsParallelEdges()).isFalse();

    addEdge(N1, N1, E11);
    IllegalArgumentException e =
        assertThrows(

    /** Array of fields that can be highlighted in search results */
    protected String[] highlightedFields;

    /** Array of fields that can be searched against */
    protected String[] searchFields;

    /** Set of fields that can be searched against for O(1) lookup */
    protected Set<String> searchFieldSet;

    /** Array of fields that can be used for faceted search */

### Required, can be `None` { #required-can-be-none }

You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.

To do that, you can declare that `None` is a valid type but simply do not declare a default value:

{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9] *}

price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

  Developers that use our General Public Licenses protect your rights

That way, the original `APIRouter` will stay unmodified, so we can still share that same `app/internal/admin.py` file with other projects in the organization.

The result is that in our app, each of the *path operations* from the `admin` module will have:

* The prefix `/admin`.
* The tag `admin`.
* The dependency `get_token_header`.
* The response `418`. 🍵

We want FastAPI to keep **filtering** the data using the response model. So that even though the function returns more data, the response will only include the fields declared in the response model.

 * Tasks execute with the same happens-before order that the function calls to {@link #submit} and
 * {@link #submitAsync} that submitted those tasks had.
 *
 * <p>This class has limited support for cancellation and other "early completions":
 *
 * <ul>
 *   <li>While calls to {@code submit} and {@code submitAsync} return a {@code Future} that can be
 *       cancelled, cancellation never propagates to a task that has started to run -- neither to