jhy/jsoup · error · ValidationException

Must be true

Error message

Must be true

What it means

Validate.isTrue(val) is a boolean assertion helper: it throws ValidationException("Must be true") when the supplied condition evaluates to false. jsoup uses it to enforce internal preconditions and invariants on inputs.

Solutions

1. Check the condition yourself before the guarded call and handle the false case gracefully
2. Loosen or correct the assumption that produced the false condition
3. Use the msg-carrying variant (isTrue(val, msg)) so failures explain which invariant broke

Example fix

// before
Validate.isTrue(elements.size() == 1); // throws on any other count
// after
if (elements.size() == 1) { process(elements.get(0)); }
else { handleUnexpectedCount(elements.size()); }

if (!condition) {
    // handle the violated precondition yourself before the guarded call
    throw new IllegalStateException("Expected condition did not hold");
}

try {
    guardedOperation();
} catch (ValidationException e) {
    if (e.getMessage().equals("Must be true")) {
        log.warn("Precondition violated; using fallback path");
        fallback();
    } else { throw e; }
}

When it happens

Trigger: Any code path (in jsoup or your own helpers built on Validate) where a required precondition is false — e.g. an assumed state of a parsed document, a required flag, or an assumed relationship between parsed values that did not hold.

Common situations: Assumptions about HTML structure that a malformed page violates; invariant checks in custom parsers built on jsoup's Validate utility; edge cases in input data that the assertion author did not anticipate.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Must be false
• msg (String.format with args)
• Pattern syntax error:
• Pattern complexity error
• Pattern syntax error:

AI-assisted analysis of jhy/jsoup@9851ac5d9c (2026-09-08). Data as JSON: /api/errors/06f281fedd88bc7d. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/org/jsoup/helper/Validate.java:82

     @param msg the String format message to include in the validation exception when thrown
     @param args the arguments to the msg
     @return the object, or throws an exception if it is null
     @throws ValidationException if the object is null
     */
    public static <T> T expectNotNull(@Nullable T obj, String msg, Object... args) {
        if (obj == null)
            throw new ValidationException(String.format(msg, args));
        else return obj;
    }

    /**
     * Validates that the value is true
     * @param val object to test
     * @throws ValidationException if the object is not true
     */
    public static void isTrue(boolean val) {
        if (!val)
            throw new ValidationException("Must be true");
    }

    /**
     * Validates that the value is true
     * @param val object to test
     * @param msg message to include in the Exception if validation fails
     * @throws ValidationException if the object is not true
     */
    public static void isTrue(boolean val, String msg) {
        if (!val)
            throw new ValidationException(msg);
    }

    /**
     * Validates that the value is false
     * @param val object to test
     * @throws ValidationException if the object is not false
     */

View on GitHub (pinned to 9851ac5d9c)