}
    };
  }

  /** Returns the children of the specified node. Must not contain null. */
  public abstract Iterable<T> children(T root);

  /**
   * Returns an unmodifiable iterable over the nodes in a tree structure, using pre-order traversal.
   * That is, each node's subtrees are traversed after the node itself is returned.
   *

import static com.google.common.collect.ReflectionFreeAssertThrows.assertThrows;
import static com.google.common.collect.testing.IteratorFeature.MODIFIABLE;
import static com.google.common.collect.testing.IteratorFeature.UNMODIFIABLE;
import static com.google.common.truth.Truth.assertThat;
import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;

     *
     * @return an unmodifiable map of user properties
     */
    @Nonnull
    Map<String, String> userProperties();

    /**
     * Returns a map of system properties for the Maven execution.
     * These include both Java system properties and Maven-specific system properties.
     *
     * @return an unmodifiable map of system properties
     */
    @Nonnull

     *     cast to doubles (with any associated lost of precision), and which will not be mutated by
     *     this call (it is copied instead)
     * @return an unmodifiable, ordered map of results: the keys will be the specified quantile
     *     indexes, and the values the corresponding quantile values. When iterating, entries in the

                                                        + cls.getName()
                                                        + "; it is an unmodifiable collection.");
                                            }
                                            continue;
                                        }

import static com.google.common.collect.ReflectionFreeAssertThrows.assertThrows;
import static com.google.common.collect.testing.IteratorFeature.MODIFIABLE;
import static com.google.common.collect.testing.IteratorFeature.UNMODIFIABLE;
import static com.google.common.truth.Truth.assertThat;
import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;

                this.rootArtifact = rootArtifact;
                this.root = root;
                this.dependencies = unmodifiable(nonNull(dependencies, "dependencies cannot be null"));
                this.managedDependencies =
                        unmodifiable(nonNull(managedDependencies, "managedDependencies cannot be null"));
                this.verbose = verbose;

   * call to {@code remove(range)}, {@code get(k)} will return {@code null}.
   */
  void remove(Range<K> range);

  /**
   * Returns a view of this range map as an unmodifiable {@code Map<Range<K>, V>}. Modifications to
   * this range map are guaranteed to read through to the returned {@code Map}.
   *
   * <p>The returned {@code Map} iterates over entries in ascending order of the bounds of the

  }

  /**
   * Returns an unmodifiable view of the specified collection, preserving the interface for
   * instances of {@code SortedSet}, {@code Set}, {@code List} and {@code Collection}, in that order
   * of preference.
   *
   * @param collection the collection for which to return an unmodifiable view
   * @return an unmodifiable view of the collection
   */

        if (obj == null) {
            throw new IllegalArgumentException(message);
        }
        return obj;
    }

    protected static <T> Collection<T> unmodifiable(Collection<T> obj) {
        return obj != null && !obj.isEmpty()
                ? Collections.unmodifiableCollection(new ArrayList<>(obj))
                : Collections.emptyList();
    }