public static Throwable getCause(final Throwable t) {
        final Throwable cause = t.getCause();
        if (Objects.isNull(cause)) {
            return t;
        }
        return cause;
    }
@Test
    void testGetCause() {
        assertEquals("I'm caused exception.", ExceptionUtil.getCause(nacosRuntimeException).getMessage());
        NacosRuntimeException nreWithoutCaused = new NacosRuntimeException(500);
        assertEquals(nreWithoutCaused, ExceptionUtil.getCause(nreWithoutCaused));
    }