checkPositionIndexes(off, off + len, str.length());
    }

    @Override
    public Writer append(@Nullable CharSequence csq) {
      return this;
    }

    @Override
    public Writer append(@Nullable CharSequence csq, int start, int end) {
      checkPositionIndexes(start, end, csq == null ? "null".length() : csq.length());
      return this;
    }

    @Override

        flushAttributes();
        builder.append(value);
        return this;
    }

    public Ansi a(CharSequence value, int start, int end) {
        flushAttributes();
        builder.append(value, start, end);
        return this;
    }

    public Ansi a(CharSequence value) {
        flushAttributes();
        builder.append(value);
        return this;
    }

    }

    private static boolean isEmpty(Object value) {
      // Put types estimated to be the most frequent first.
      if (value instanceof CharSequence) {
        return ((CharSequence) value).length() == 0;
      } else if (value instanceof Collection) {
        return ((Collection<?>) value).isEmpty();
      } else if (value instanceof Map) {

  })
  public void testRepeat_null() {
    assertThrows(NullPointerException.class, () -> Strings.repeat(null, 5));
  }

  @SuppressWarnings("UnnecessaryStringBuilder") // We want to test a non-String CharSequence
  public void testCommonPrefix() {
    assertThat(Strings.commonPrefix("", "")).isEqualTo("");
    assertThat(Strings.commonPrefix("abc", "")).isEqualTo("");
    assertThat(Strings.commonPrefix("", "abc")).isEqualTo("");

        Object writeReplace() {
      return super.writeReplace();
    }
  }

  private static final class CharSequenceAsList extends AbstractList<Character> {
    private final CharSequence sequence;

    CharSequenceAsList(CharSequence sequence) {
      this.sequence = sequence;
    }

    @Override
    public Character get(int index) {
      checkElementIndex(index, size()); // for GWT

       * built-in nullness feature?
       */
      "ExtendsObject",
    })
    <T extends Object> void withObjectBound(List<T> list) {}

    @SuppressWarnings("unused")
    <T extends Number & CharSequence> void withUpperBound(List<T> list) {}

    static TypeVariable<?> getTypeVariable(String methodName) throws Exception {
      ParameterizedType parameterType =
          (ParameterizedType)

  private static final Appendable NASTY_APPENDABLE =
      new Appendable() {
        @Override
        public Appendable append(@Nullable CharSequence csq) throws IOException {
          throw new IOException();
        }

        @Override
        public Appendable append(@Nullable CharSequence csq, int start, int end)
            throws IOException {
          throw new IOException();
        }

        @Override

    }
    if (cp >= safeMin && cp <= safeMax) {
      return null;
    }
    return escapeUnsafe(cp);
  }

  /* Overridden for performance. */
  @Override
  protected final int nextEscapeIndex(CharSequence csq, int index, int end) {
    while (index < end) {
      char c = csq.charAt(index);
      if ((c < replacementsLength && replacements[c] != null)
          || c > safeMaxChar
          || c < safeMinChar) {

      return delegate.toString();
    }
  }

  public void testCovariantReturn() {
    new ForwardingWrapperTester().testForwarding(Sub.class, ForwardingSub::new);
  }

  interface Base {
    CharSequence getId();
  }

  interface Sub extends Base {
    @Override
    String getId();
  }

  private static final class ForwardingSub implements Sub {
    private final Sub delegate;

            .omitEmptyValues()
            // CharSequences
            .add("field1", "")
            .add("field2", new StringBuilder())
            // nio CharBuffer (implements CharSequence) is tested separately below
            // Collections and Maps
            .add("field11", Arrays.asList("Hello"))
            .add("field12", new ArrayList<>())
            .add("field13", new HashMap<>())