V value = values.next();
      builder.put(keyFunction.apply(value), value);
    }
    try {
      return builder.buildOrThrow();
    } catch (IllegalArgumentException duplicateKeys) {
      throw new IllegalArgumentException(
          duplicateKeys.getMessage()
              + ". To index multiple values under a key, use Multimaps.index.");
    }
  }

  /**

      V value = values.next();
      builder.put(keyFunction.apply(value), value);
    }
    try {
      return builder.buildOrThrow();
    } catch (IllegalArgumentException duplicateKeys) {
      throw new IllegalArgumentException(
          duplicateKeys.getMessage()
              + ". To index multiple values under a key, use Multimaps.index.");
    }
  }

  /**

  @Test
  fun requestHeaderValidationIsStrict() {
    assertFailsWith<IllegalArgumentException> {
      Request
        .Builder()
        .addHeader("a\tb", "Value")
    }
    assertFailsWith<IllegalArgumentException> {
      Request
        .Builder()
        .addHeader("Name", "c\u007fd")
    }
    assertFailsWith<IllegalArgumentException> {
      Request
        .Builder()

        if (dest == null) {
            throw new IllegalArgumentException("Destination cannot be null");
        }
        if (b == null || b.length == 0) {
            throw new IllegalArgumentException("Buffer array cannot be null or empty");
        }
        if (bsize <= 0) {
            throw new IllegalArgumentException("Buffer size must be positive");
        }

        try {

    assertFailsWith<IllegalArgumentException> {
      requestBuilder.url("ftp://hostname/path")
    }.also { expected ->
      assertThat(expected.message).isEqualTo("Expected URL scheme 'http' or 'https' but was 'ftp'")
    }
  }

  @Test
  fun invalidPort() {
    val requestBuilder = Request.Builder()
    assertFailsWith<IllegalArgumentException> {
      requestBuilder.url("http://localhost:65536/")

     */
    protected void assertPropertyNotNull(String property) {
        if (property == null) {
            String msg = "The argument 'property' for message should not be null.";
            throw new IllegalArgumentException(msg);
        }
    }