import java.util.stream.Collector;
import java.util.stream.Collectors;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A {@link BiMap} whose contents will never change, with many other important properties detailed
 * at {@link ImmutableCollection}.
 *
 * @author Jared Levy
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
@ElementTypesAreNonnullByDefault

     *
     * @param project {@link Project} or {@code null}.
     * @return the effective properties, never {@code null}
     */
    @Nonnull
    Map<String, String> getEffectiveProperties(@Nullable Project project);

    /**
     * Returns the current maven version
     * @return the maven version, never {@code null}
     */
    @Nonnull
    Version getMavenVersion();

    int getDegreeOfConcurrency();

    throw new AssertionError("should never be called");
  }

  @Override
  public ImmutableCollection<V> values() {
    return (ImmutableCollection<V>) super.values();
  }

  @Override
  abstract ImmutableCollection<V> createValues();

  @Override
  final Iterator<V> valuesIterator() {
    throw new AssertionError("should never be called");
  }

  /**
   * {@inheritDoc}

      checkNotNull(element);
      copyIfNecessary();
      if (n == elements.length) {
        sortAndDedup();
        /*
         * Sorting operations can only be allowed to occur once every O(n) operations to keep
         * amortized O(n log n) performance.  Therefore, ensure there are at least O(n) *unused*
         * spaces in the builder array.
         */

   * time a task is submitted.
   *
   * <p>When an {@code Error} is thrown by an executed task, previously submitted tasks may never
   * run. An attempt will be made to restart execution on the next call to {@code execute}. If the
   * {@code delegate} has begun to reject execution, the previously submitted tasks may never run,
   * despite not throwing a RejectedExecutionException synchronously with the call to {@code

   * the underlying collection.
   *
   * <p>The returned collection isn't threadsafe or serializable, even if {@code unfiltered} is.
   *
   * <p>Many of the filtered collection's methods, such as {@code size()}, iterate across every
   * element in the underlying collection and determine which elements satisfy the filter. When a
   * live view is <i>not</i> needed, it may be faster to copy {@code Iterables.filter(unfiltered,
   * predicate)} and use the copy.

          return invokeGeneratorMethod(emptyGenerate);
        } else {
          // Cannot use empty generator. Proceed with other generators.
        }
      } else {
        // never generated empty instance for this type before.
        Object emptyInstance = invokeGeneratorMethod(emptyGenerate);
        emptyInstanceGenerated.put(type.getType(), freshness.get());
        return emptyInstance;
      }

      }
      if (advanceSlowPointer) {
        slowPointer = slowPointer.getCause();
      }
      advanceSlowPointer = !advanceSlowPointer; // only advance every other iteration
    }
    return throwable;
  }

  /**
   * Gets a {@code Throwable} cause chain as a list. The first entry in the list will be {@code

      }
      if (advanceSlowPointer) {
        slowPointer = slowPointer.getCause();
      }
      advanceSlowPointer = !advanceSlowPointer; // only advance every other iteration
    }
    return throwable;
  }

  /**
   * Gets a {@code Throwable} cause chain as a list. The first entry in the list will be {@code

   *
   * <p>The returned multiset isn't threadsafe or serializable, even if {@code unfiltered} is.
   *
   * <p>Many of the filtered multiset's methods, such as {@code size()}, iterate across every
   * element in the underlying multiset and determine which elements satisfy the filter. When a live
   * view is <i>not</i> needed, it may be faster to copy the returned multiset and use the copy.
   *