public T multiply(BigDecimal multiplier) {
        return create(value.multiply(multiplier));
    }
@Test
    void testMutiplyNegative() {
        final Resource resource = new TestResource(0.3);
        final BigDecimal by = BigDecimal.valueOf(-0.2);
        assertThatThrownBy(() -> resource.multiply(by))
                .isInstanceOf(IllegalArgumentException.class);
    }