</goals>
          </execution>
        </executions>
        <configuration>
          <instructions>
            <Export-Package>
              !com.google.common.base.internal,
              !com.google.common.util.concurrent.internal,
              com.google.common.*
            </Export-Package>
            <Import-Package>
              com.google.common.util.concurrent.internal,

-   [A nice collection](https://www.tfnico.com/presentations/google-guava) of
    other helpful links

## Links

-   [GitHub project](https://github.com/google/guava)
-   [Issue tracker: Report a defect or feature request](https://github.com/google/guava/issues/new)
-   [StackOverflow: Ask "how-to" and "why-didn't-it-work" questions](https://stackoverflow.com/questions/ask?tags=guava+java)

            .put("SEC_WEBSOCKET_PROTOCOL", "Sec-WebSocket-Protocol")
            .put("SEC_WEBSOCKET_VERSION", "Sec-WebSocket-Version")
            .put("X_WEBKIT_CSP", "X-WebKit-CSP")
            .put("X_WEBKIT_CSP_REPORT_ONLY", "X-WebKit-CSP-Report-Only")
            .buildOrThrow();
    ImmutableSet<String> uppercaseAcronyms =
        ImmutableSet.of(
            "CH", "ID", "DNT", "DNS", "DPR", "ECT", "GPC", "HTTP2", "IP", "MD5", "P3P", "RTT", "TE",

To add a dependency using Gradle:

```gradle
dependencies {
  test 'com.google.guava:guava-testlib:33.1.0-jre'
}
```

## Links

-   [GitHub project](https://github.com/google/guava)
-   [Issue tracker: Report a defect or feature request](https://github.com/google/guava/issues/new)
-   [StackOverflow: Ask "how-to" and "why-didn't-it-work" questions](https://stackoverflow.com/questions/ask?tags=guava+java)

            </goals>
          </execution>
        </executions>
        <configuration>
          <instructions>
            <Export-Package>
              !com.google.common.base.internal,
              !com.google.common.util.concurrent.internal,
              com.google.common.*
            </Export-Package>
            <Import-Package>
              com.google.common.util.concurrent.internal,

   */
  @SuppressWarnings("unchecked")
  public static <T extends @Nullable Object> Collector<T, ?, T> onlyElement() {
    return (Collector) ONLY_ELEMENT;
  }

  /**
   * This atrocity is here to let us report several of the elements in the stream if there were more
   * than one, not just two.
   */
  private static final class ToOptionalState {
    static final int MAX_EXTRAS = 4;

    @CheckForNull Object element;