os_tmr_create() doesn't work

I used os_tmr_create().
But, always return value is NULL!!
Why!!?

I saw os_tmr_create() defined in rt_Timer.c file.
There is the following codes in the first conditional expression.

if (tcnt == 0 || m_tmr == NULL) { return (NULL);
}

I think that the return value becomes NULL because "m_tmr" is NULL.
How can I set the value to "m_tmr"?

Someone helps.