return nullify(metadata.getGroupId());
        }

        public String getArtifactId() {
            return nullify(metadata.getArtifactId());
        }

        public String getBaseVersion() {
            return nullify(metadata.getVersion());
        }

        private String nullify(String str) {
            return (str == null || str.isEmpty()) ? null : str;
        }

 *
 */
public class RepositoryUtils {

    private static String nullify(String string) {
        return (string == null || string.isEmpty()) ? null : string;
    }

    private static org.apache.maven.artifact.Artifact toArtifact(Dependency dependency) {
        if (dependency == null) {
            return null;
        }

    // [[null, null], [null], [1, null, 2], [1, 1], [1, 2], [1], [2], [], null]
    assertThat(sorted)
        .containsExactly(
            Lists.<@Nullable Integer>newArrayList(nullInt, nullInt),
            Lists.<@Nullable Integer>newArrayList(nullInt),
            Lists.<@Nullable Integer>newArrayList(1, null, 2),
            Lists.newArrayList(1, 1),
            Lists.newArrayList(1, 2),

    // [[null, null], [null], [1, null, 2], [1, 1], [1, 2], [1], [2], [], null]
    assertThat(sorted)
        .containsExactly(
            Lists.<@Nullable Integer>newArrayList(nullInt, nullInt),
            Lists.<@Nullable Integer>newArrayList(nullInt),
            Lists.<@Nullable Integer>newArrayList(1, null, 2),
            Lists.newArrayList(1, 1),
            Lists.newArrayList(1, 2),

       * We store `localFuturesOrNull` inside the listener because `this.futures` might be nulled
       * out by the time the listener runs for the final future -- at which point we need to check
       * all inputs for exceptions *if* we're collecting values. If we're not, then the listener
       * doesn't need access to the futures again, so we can just pass `null`.
       *

   *       C}, instance methods are skipped for nulls test.
   *   <li>Nulls test is not performed on method return values unless the method is a visible static
   *       factory method whose return type is {@code C} or {@code C}'s subtype.
   * </ul>
   *
   * <p>In all cases, if {@code C} needs custom logic for testing nulls, you can add an explicit

        current.elemCount = 0;
        // Also clear these fields so that one deleted Entry doesn't retain all elements.
        current.left = null;
        current.right = null;
        current.pred = null;
        current.succ = null;

        current = next;
      }
      successor(header, header);
      rootReference.clear();
    } else {

    assertTrue("add(null) should return true", collection.add(null));
    expectAdded((E) null);
  }

  @CollectionFeature.Require(value = SUPPORTS_ADD, absent = ALLOWS_NULL_VALUES)
  public void testAdd_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> collection.add(null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported add(null)");
  }

    assertTrue("add(null) should return true", collection.add(null));
    expectAdded((E) null);
  }

  @CollectionFeature.Require(value = SUPPORTS_ADD, absent = ALLOWS_NULL_VALUES)
  public void testAdd_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> collection.add(null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported add(null)");
  }

    return asImmutableList(array);
  }

  /** Views the array as an immutable list. Checks for nulls; does not copy. */
  private static <E> ImmutableList<E> construct(Object... elements) {
    return asImmutableList(checkElementsNotNull(elements));
  }

  /**
   * Views the array as an immutable list. Does not check for nulls; does not copy.
   *
   * <p>The array must be internally created.
   */