* reasonable and it will be fine.
 *
 * <ul>
 *   <li>If checking whether the <i>caller</i> has violated your method or constructor's contract
 *       (such as by passing an invalid argument), use the utilities of the {@link Preconditions}
 *       class instead.
 *   <li>If checking an <i>impossible</i> condition (which <i>cannot</i> happen unless your own

  }

  /**
   * Performs {@link NullPointerTester} checks for all top-level classes in the package. For a class
   * {@code C}
   *
   * <ul>
   *   <li>All visible static methods are checked such that passing null for any parameter that's
   *       not annotated nullable (according to the rules of {@link NullPointerTester}) should throw
   *       {@link NullPointerException}.

   *
   * @param formal The type whose type variables or itself is mapped to other type(s). It's almost
   *     always a bug if {@code formal} isn't a type variable and contains no type variable. Make
   *     sure you are passing the two parameters in the right order.
   * @param actual The type that the formal type variable(s) are mapped to. It can be or contain yet
   *     other type variables, in which case these type variables will be further resolved if

We can declare all that without having to modify the original `APIRouter` by passing those parameters to `app.include_router()`:

{* ../../docs_src/bigger_applications/app_an_py39/main.py hl[14:17] title["app/main.py"] *}

   * elements.
   *
   * <p>To cycle over the elements {@code n} times, use the following: {@code
   * Iterables.concat(Collections.nCopies(n, Arrays.asList(elements)))}
   *
   * <p><b>Java 8+ users:</b> If passing a single element {@code e}, the {@code Stream} equivalent
   * of this method is {@code Stream.generate(() -> e)}. Otherwise, put the elements in a collection

| _Required_    | _No_                                               |

### Policy

      Throwable cause = e.getCause();
      if (policy.isExpectedType(cause)) {
        return;
      }
      throw new AssertionError(
          String.format(
              "wrong exception thrown from %s when passing null to %s parameter at index %s.%n"
                  + "Full parameters: %s%n"
                  + "Actual exception message: %s",
              invokable,
              invokable.getParameters().get(paramIndex).getType(),

   *
   * @param formal The type whose type variables or itself is mapped to other type(s). It's almost
   *     always a bug if {@code formal} isn't a type variable and contains no type variable. Make
   *     sure you are passing the two parameters in the right order.
   * @param actual The type that the formal type variable(s) are mapped to. It can be or contain yet
   *     other type variables, in which case these type variables will be further resolved if

      Throwable cause = e.getCause();
      if (policy.isExpectedType(cause)) {
        return;
      }
      throw new AssertionError(
          String.format(
              "wrong exception thrown from %s when passing null to %s parameter at index %s.%n"
                  + "Full parameters: %s%n"
                  + "Actual exception message: %s",
              invokable,
              invokable.getParameters().get(paramIndex).getType(),

       <artifactId>okio</artifactId>
       <version>1.4.0</version>
     </dependency>
     ```

 *  **`Request.Builder` no longer accepts null if a request body is required.**
    Passing null will now fail for request methods that require a body. Instead
    use an empty body such as this one:

    ```java
        RequestBody.create(null, new byte[0]);
    ```