assertTrue(h.isValid());

        // Tree id change makes it invalid
        when(tree.getTreeId()).thenReturn(11L);
        assertFalse(h.isValid());

        // Connected=false makes it invalid
        when(tree.getTreeId()).thenReturn(10L);
        when(tree.isConnected()).thenReturn(false);
        assertFalse(h.isValid());

        // Mark closed makes it invalid
        when(tree.isConnected()).thenReturn(true);

```
.
├── app                  # "app" is a Python package
│   ├── __init__.py      # this file makes "app" a "Python package"
│   ├── main.py          # "main" module, e.g. import app.main
│   ├── dependencies.py  # "dependencies" module, e.g. import app.dependencies
│   └── routers          # "routers" is a "Python subpackage"
│   │   ├── __init__.py  # makes "routers" a "Python subpackage"

> Modern versions of Python have support for **"asynchronous code"** using something called **"coroutines"**, with **`async` and `await`** syntax.

That should make more sense now. ✨

All that is what powers FastAPI (through Starlette) and what makes it have such an impressive performance.

## Very Technical Details { #very-technical-details }

/// warning

You can probably skip this.

        } else {
          continue; // delete this entry; we already copied an earlier one for the same key
        }
      }
      newEntries[out++] = entry;
    }
    return newEntries;
  }

  /** Makes an entry usable internally by a new ImmutableMap without rereading its contents. */
  static <K, V> ImmutableMapEntry<K, V> makeImmutable(Entry<K, V> entry, K key, V value) {
    boolean reusable =

```
.
├── app                  # "app" is a Python package
│   ├── __init__.py      # this file makes "app" a "Python package"
│   ├── main.py          # "main" module, e.g. import app.main
│   ├── dependencies.py  # "dependencies" module, e.g. import app.dependencies
│   └── routers          # "routers" is a "Python subpackage"
│   │   ├── __init__.py  # makes "routers" a "Python subpackage"

  sufficient copyright rights in its Contribution, if any, to grant
  the copyright license set forth in this Agreement.

  e) Notwithstanding the terms of any Secondary License, no
  Contributor makes additional grants to any Recipient (other than
  those set forth in this Agreement) as a result of such Recipient's
  receipt of the Program under the terms of a Secondary License
  (if permitted under the terms of Section 3).

/// note

Having a default value of any type, including `None`, makes the parameter optional (not required).

///

## Required parameters { #required-parameters }

When we don't need to declare more validations or metadata, we can make the `q` query parameter required just by not declaring a default value, like:

```Python
q: str
```

instead of:

    `Headers` class offers full access to the HTTP headers.

 *  **Okio dependency added.** OkHttp now depends on
    [Okio](https://github.com/square/okio), an I/O library that makes it easier
    to access, store and process data. Using this library internally makes OkHttp
    faster while consuming less memory. You can write a `RequestBody` as an Okio
    `BufferedSink` and a `ResponseBody` as an Okio `BufferedSource`. Standard

But I'll show you how to improve that next. 🤓

## Custom Operation IDs and Better Method Names { #custom-operation-ids-and-better-method-names }

You can **modify** the way these operation IDs are **generated** to make them simpler and have **simpler method names** in the clients.

  /** Use {@link MoreExecutors#newSequentialExecutor} */
  SequentialExecutor(Executor executor) {
    this.executor = Preconditions.checkNotNull(executor);
  }

  /**
   * Adds a task to the queue and makes sure a worker thread is running.
   *
   * <p>If this method throws, e.g. a {@code RejectedExecutionException} from the delegate executor,
   * execution of tasks will stop until a call to this method is made.
   */