usb.c complete function : why no crash?

[Om <okuttan@xxxxxxxx>]

Hi,
using linux 2.4.27.
In arch/drivers/usb.c,usb_internal_control_msg() create one control urb 
with completion function as usb_api_blocking_completion()  and context 
to be 0.

From the include/linux/usb.h,
struct urb
{
spinlock_t lock;        // lock for the URB
<snip>
void *context;          // context for completion routine
usb_complete_t complete;    // pointer to completion routine
//
}

I assume that upon completion, funtion pointer complete will be called 
with parameter context.
i.e, usb_api_blocking_completion(0)  will be called.

but,
usb.c : usb_api_blocking_completion(struct urb *urb) {
struct usb_api_data *awd = (struct usb_api_data *)urb->context;

    awd->done = 1;
    wmb();
    wake_up(&awd->wqh);
}
If the value of urb is NULL, this function will crash. But this does not 
happen.
Am I missing something?

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