List<BuilderProblem> problems, String fieldName, String string, String sourceHint) {
        if (!validateNotNull(problems, fieldName, string, sourceHint)) {
            return false;
        }

        if (!string.isEmpty()) {
            return true;
        }

        addViolation(problems, BuilderProblem.Severity.ERROR, fieldName, sourceHint, "is missing");

        return false;
    }

    /**

            String fieldName,
            String sourceHint,
            String message,
            InputLocationTracker tracker) {
        StringBuilder buffer = new StringBuilder(256);
        buffer.append('\'').append(fieldName).append('\'');

        if (sourceHint != null) {
            buffer.append(" for ").append(sourceHint);
        }

        buffer.append(' ').append(message);