public static String toLowerCase(@Nullable String value) {
        if (value == null) {
            throw new IllegalArgumentException("String value cannot be null");
        }
        return value.toLowerCase(Locale.ENGLISH);
    }
@Test
    public void testToLowerCase() {
        //noinspection DataFlowIssue
        assertThatThrownBy(() -> toLowerCase(null)).isInstanceOf(IllegalArgumentException.class);
        assertThat(toLowerCase("")).isEqualTo("");
        assertThat(toLowerCase(" ")).isEqualTo(" ");
        assertThat(toLowerCase("Hello")).isEqualTo("hello");
    }