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;
    }

    /**