jhy/jsoup · error · ValidationException

Must be false

Error message

Must be false

What it means

Validate.isFalse(val) is the mirror of isTrue: it throws ValidationException("Must be false") when the supplied boolean condition is true. It enforces negative preconditions, i.e. states that must not hold.

Solutions

1. Evaluate the forbidden condition yourself before the call and take the appropriate branch
2. Fix whatever state caused the condition to become true
3. Use isFalse(val, msg) to record which negative invariant was violated

Example fix

// before
Validate.isFalse(doc.getElementsByTag("script").isEmpty() == false); // scripts present
// after
if (doc.getElementsByTag("script").isEmpty()) { process(doc); }
else { sanitize(doc); }

if (forbiddenCondition) {
    // remediate: deduplicate, sanitize, or reject before the guarded call
    return;
}

try {
    guardedOperation();
} catch (ValidationException e) {
    if (e.getMessage().equals("Must be false")) {
        log.warn("Forbidden state detected; skipping");
    } else { throw e; }
}

When it happens

Trigger: Code that asserts something must NOT be the case — e.g. an element must not already exist, a flag must not be set, or a parsed value must not indicate an error condition — and the condition is in fact true at runtime.

Common situations: Guard clauses against duplicate inserts or forbidden states in code built on jsoup's Validate; document states the author assumed impossible but that malformed input produced.

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 true
• 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/7e5ae5bdf136db91. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/org/jsoup/helper/Validate.java:103

    /**
     * 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
     */
    public static void isFalse(boolean val) {
        if (val)
            throw new ValidationException("Must be false");
    }

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

    /**
     * Validates that the array contains no null elements
     * @param objects the array to test
     * @throws ValidationException if the array contains a null element
     */

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