throw new UnsupportedOperationException("checkUserLoginable is not supported.");
    }

    /**
     * Checks the credential using the provided credential checker.
     * This method is not supported in the Fess implementation.
     *
     * @param checker the credential checker to use
     * @throws UnsupportedOperationException always thrown as this method is not supported
     */
    @Override

              public void close() throws IOException {
                super.close();
                counter[0]--;
              }
            };
          }
        };
    byte[] result = ByteSource.concat(checker, checker, checker).read();
    assertEquals(150, result.length);
  }

  private void joinHelper(Integer... spans) throws Exception {
    List<ByteSource> sources = new ArrayList<>();
    int start = 0;

not use beta APIs, unless you [repackage] them. **If your
code is a library, we strongly recommend using the [Guava Beta Checker] to
ensure that you do not use any `@Beta` APIs!**

[Guava Beta Checker]: https://github.com/google/guava-beta-checker

<!-- References -->

              public void close() throws IOException {
                super.close();
                counter[0]--;
              }
            };
          }
        };
    byte[] result = ByteSource.concat(checker, checker, checker).read();
    assertEquals(150, result.length);
  }

  private void joinHelper(Integer... spans) throws Exception {
    List<ByteSource> sources = new ArrayList<>();
    int start = 0;

[guava-snapshot-api-diffs]: https://guava.dev/releases/snapshot-jre/api/diffs/
[Guava Explained]: https://github.com/google/guava/wiki/Home
[Guava Beta Checker]: https://github.com/google/guava-beta-checker

<!-- References -->

[using Guava in your build]: https://github.com/google/guava/wiki/UseGuavaInYourBuild

    /*
     * We can't simply cast the result of `RegularImmutableMap.get` to V because of a bug in our
     * nullness checker (resulting from https://github.com/jspecify/checker-framework/issues/8).
     */
    if (result == null) {
      return null;
    } else {
      return (V) result;
    }
  }

  @Override

   * https://github.com/jspecify/jspecify-reference-checker/blob/61aafa4ae52594830cfc2d61c8b113009dbdb045/src/main/java/com/google/jspecify/nullness/NullSpecTransfer.java#L789
   * and https://github.com/jspecify/jspecify/issues/490.
   *
   * (Perhaps it should also have required that its cause was a RuntimeException. However, that
   * would have required that we throw a different kind of exception for wrapping *checked*

                }),
        (accum, t) -> {
          /*
           * We assign these to variables before calling checkNotNull to work around a bug in our
           * nullness checker.
           */
          K key = keyFunction.apply(t);
          V newValue = valueFunction.apply(t);
          accum.put(
              checkNotNull(key, "Null key for input %s", t),

      }
    }

    /*
     * TODO(cpovirk): `return (V) removedValue` once our checker permits that.
     *
     * (We promoted a class of warnings into errors because sometimes they indicate real problems.
     * But now we need to "undo" some instance of spurious errors, as discussed in
     * https://github.com/jspecify/checker-framework/issues/8.)
     */
    return removedValue == null ? null : (V) removedValue;
  }

                }),
        (accum, t) -> {
          /*
           * We assign these to variables before calling checkNotNull to work around a bug in our
           * nullness checker.
           */
          K key = keyFunction.apply(t);
          V newValue = valueFunction.apply(t);
          accum.put(
              checkNotNull(key, "Null key for input %s", t),