Macos - CFStringGetLength EXC_BAD_ACCESS (SIGSEGV) crash

Question

I have the following code:

char *get_string_property_2(IOHIDDeviceRef device, CFStringRef prop)
{

    CFStringRef str = IOHIDDeviceGetProperty(device, prop);

    if(str)
    {
         CFIndex str_len = CFStringGetLength(str);
         ...

    }

    ...
}

sometimes (not always) I get a crash in CFStringGetLengthwith the following log:

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x00007fff770083a8

Thread 8 Crashed:
0   libobjc.A.dylib                 0x00007fff88e22097 objc_msgSend + 23
1   libtobii_usb.dylib              0x00000001081c4f72 get_string_property_2 + 130 (macosx.c:99)
2   serviced                        0x00000001081a5fad device_removed_callback + 285 (daemond_mac.c:614)
3   libsystem_pthread.dylib         0x00007fff8ae35899 _pthread_body + 138
4   libsystem_pthread.dylib         0x00007fff8ae3572a _pthread_start + 137
5   libsystem_pthread.dylib         0x00007fff8ae39fc9 thread_start + 13

How can i fix this? I check if str is NULL or not before the call CFStringGetLength, apparently this is not enough.

EDIT:

I still get this crash, always in the same place.

If this is a bad pointer, why doesn't one line break above in IOHIDDeviceGetProperty??

Is there any other way that I can get the length CFStringRef?

I suspect there is an error in the api.