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