I think `Union[SomeType, None]` is more explicit about what it means.

It's just about the words and names. But those words can affect how you and your teammates think about the code.

As an example, let's take this function:

{* ../../docs_src/python_types/tutorial009c_py39.py hl[1,4] *}

### OpenID (not "OpenID Connect") { #openid-not-openid-connect }

There was also an "OpenID" specification. That tried to solve the same thing as **OpenID Connect**, but was not based on OAuth2.

So, it was a complete additional system.

It is not very popular or used nowadays.

## OpenAPI { #openapi }

OpenAPI (previously known as Swagger) is the open specification for building APIs (now part of the Linux Foundation).

import okio.ByteString.Companion.encodeUtf8
import okio.IOException
import okio.Source
import okio.buffer

class ResponseBodyTest {
  @Test
  fun sourceEmpty() {
    val mediaType = if (null == null) null else "any/thing; charset=${null}".toMediaType()
    val body = "".decodeHex().toResponseBody(mediaType)
    val source = body.source()
    assertThat(source.exhausted()).isTrue()
    assertThat(source.readUtf8()).isEqualTo("")
  }

The main logic with ADRs is to describe (architectural) decisions made:

* To provide best practices and solutions we (as the *build tool* team) want to promote.
* To avoid asking the same thing multiple times during code review.
* To explain *rejected solutions*, for now, and future development, in case they are proposed again.

ADRs can be written by any team.

In previous versions of NodeJS / Browser JavaScript, you would have used "callbacks". Which leads to "callback hell".

## Coroutines { #coroutines }

## Pin your `fastapi` version { #pin-your-fastapi-version }

The first thing you should do is to "pin" the version of **FastAPI** you are using to the specific latest version that you know works correctly for your application.

For example, let's say you are using version `0.112.0` in your app.

   * `new Integer` (as we do) instead of `Integer.valueOf`. However, under J2KT, `new Integer`
   * gets translated back to `Integer.valueOf` because that is the only thing J2KT can support. And
   * anyway, it's nice to avoid `Integer.valueOf` because the Android toolchain optimizes multiple
   * `Integer.valueOf` calls into one! So we stick with the deprecated `Integer` constructor.
   */

The `scope` `dict` and `receive` function are both part of the ASGI specification.

And those two things, `scope` and `receive`, are what is needed to create a new `Request` instance.

To learn more about the `Request` check <a href="https://www.starlette.dev/requests/" class="external-link" target="_blank">Starlette's docs about Requests</a>.

///

 * (like 0030..0039).
 *
 * The second element on each line is a mapping type, like `valid` or `mapped`.
 *
 * For lines that contain a mapping target, the next thing is a sequence of hex code points (like
 * 0031 2044 0034).
 *
 * All other data is ignored.
 */
fun BufferedSource.readPlainTextIdnaMappingTable(): SimpleIdnaMappingTable {
  val mappedTo = Buffer()

This is the basic idea. But you will probably want to take care of some additional things, like:

* Security - HTTPS
* Running on startup
* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting