Iterator<? extends N> top = horizon.getFirst();
          while (top.hasNext()) {
            N element = top.next();
            // requireNonNull is safe because horizon contains only graph nodes.
            /*
             * TODO(cpovirk): Replace these two statements with one (`N element =
             * requireNonNull(top.next())`) once our checker supports it.
             *

  private static final ImmutableSet<String> TOP_UNDER_REGISTRY_SUFFIX =
      ImmutableSet.of("google.com", "foo.Co.uk", "foo.ca.us.");

  private static final ImmutableSet<String> TOP_PRIVATE_DOMAIN =
      ImmutableSet.of("google.com", "foo.Co.uk", "foo.ca.us.", "foo.blogspot.com");

  private static final ImmutableSet<String> UNDER_TOP_UNDER_REGISTRY_SUFFIX =

  private static final ImmutableSet<String> TOP_UNDER_REGISTRY_SUFFIX =
      ImmutableSet.of("google.com", "foo.Co.uk", "foo.ca.us.");

  private static final ImmutableSet<String> TOP_PRIVATE_DOMAIN =
      ImmutableSet.of("google.com", "foo.Co.uk", "foo.ca.us.", "foo.blogspot.com");

  private static final ImmutableSet<String> UNDER_TOP_UNDER_REGISTRY_SUFFIX =

    TopKSelector<Integer> top = TopKSelector.least(0);
    for (int i = 0; i < 10; i++) {
      top.offer(i);
    }
    assertThat(top.topK()).isEmpty();
  }

  public void testNoElementsOffered() {
    TopKSelector<Integer> top = TopKSelector.least(10);
    assertThat(top.topK()).isEmpty();
  }

  public void testOfferedFewerThanK() {
    TopKSelector<Integer> top = TopKSelector.least(10);
    top.offer(3);

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible