languagetool-org/languagetool · error · IllegalArgumentException

${varName} cannot be empty or whitespace only

Error message

${varName} cannot be empty or whitespace only

What it means

A guard in StringTools.assureSet that rejects a required argument: the variable named by varName was null, empty, or only whitespace when a non-blank value is mandatory.

Source

Thrown at languagetool-core/src/main/java/org/languagetool/tools/StringTools.java:139

      "kein", "keines", "keinem", "keinen", "keiner", "keine"))
  );
  private static final Set<String> DUTCH_TITLECASE_EXCEPTIONS = Collections.unmodifiableSet(
    new HashSet<>(Arrays.asList("van", "in", "de", "het", "een", "en", "of"))
  );

  private static final Set<String> ALL_TITLECASE_EXCEPTIONS = collectAllTitleCaseExceptions();

  private StringTools() {
    // only static stuff
  }

  /**
   * Throw exception if the given string is null or empty or only whitespace.
   */
  public static void assureSet(String s, String varName) {
    Objects.requireNonNull(varName);
    if (isEmpty(s.trim())) {
      throw new IllegalArgumentException(varName + " cannot be empty or whitespace only");
    }
  }

  /**
   * Read the text stream using the given encoding.
   *
   * @param stream InputStream the stream to be read
   * @param encoding the stream's character encoding, e.g. {@code utf-8}, or {@code null} to use the system encoding
   * @return a string with the stream's content, lines separated by {@code \n} (note that {@code \n} will
   *  be added to the last line even if it is not in the stream)
   * @since 2.3
   */
  public static String readStream(InputStream stream, String encoding) throws IOException {
    InputStreamReader isr = null;
    StringBuilder sb = new StringBuilder();
    try {
      if (encoding == null) {
        isr = new InputStreamReader(stream);

View on GitHub (pinned to 2e990059ce)

Solutions

1. Pass a non-empty, non-whitespace-only value for the offending argument
2. Validate user input before calling assureSet and prompt for a real value

When it happens

Trigger: Thrown at languagetool-core/src/main/java/org/languagetool/tools/StringTools.java:139 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/e23d2f740412e36b. Report an issue: GitHub.