import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Maps.newTreeMap;
import static java.util.Collections.singletonMap;
import static java.util.Collections.unmodifiableSortedMap;

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

                SortedMap<String, String> map = populate(new TreeMap<String, String>(), entries);
                return Collections.unmodifiableSortedMap(map);
              }
            })
        .named("unmodifiableSortedMap/TreeMap, natural")
        .withFeatures(
            MapFeature.ALLOWS_NULL_VALUES,
            CollectionFeature.KNOWN_ORDER,
            CollectionFeature.SERIALIZABLE,

import static com.google.common.collect.NullnessCasts.uncheckedCastNullableTToT;
import static java.util.Collections.unmodifiableMap;
import static java.util.Collections.unmodifiableSortedMap;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.base.Function;

      comparator = (Comparator<? super K>) NATURAL_ORDER;
    }
    if (map instanceof ImmutableSortedMap) {
      // TODO(kevinb): Prove that this cast is safe, even though
      // Collections.unmodifiableSortedMap requires the same key type.
      @SuppressWarnings("unchecked")
      ImmutableSortedMap<K, V> kvMap = (ImmutableSortedMap<K, V>) map;
      if (!kvMap.isPartialView()) {
        return kvMap;
      }
    }

    }
  }

  private static <K extends @Nullable Object, V extends @Nullable Object> Map<K, V> unmodifiableMap(
      Map<K, ? extends V> map) {
    if (map instanceof SortedMap) {
      return Collections.unmodifiableSortedMap((SortedMap<K, ? extends V>) map);
    } else {
      return Collections.unmodifiableMap(map);
    }
  }

  private static class MapDifferenceImpl<K extends @Nullable Object, V extends @Nullable Object>

    }
  }

  private static <K extends @Nullable Object, V extends @Nullable Object> Map<K, V> unmodifiableMap(
      Map<K, ? extends V> map) {
    if (map instanceof SortedMap) {
      return Collections.unmodifiableSortedMap((SortedMap<K, ? extends V>) map);
    } else {
      return Collections.unmodifiableMap(map);
    }
  }

  private static class MapDifferenceImpl<K extends @Nullable Object, V extends @Nullable Object>