I chuckled at this one.
If you head over to the definition of
, you'll see something like this
LCB_OBSERVE_FOUND = 0x00
The observe callback is invoked the last time with what's called a "NULL" response. This response contains NULL for key, 0 for nkey etc. etc. and signals that there are no longer any OBSERVE responses for the particular operation (typically defined by the cookie) to be invoked.
You are likely not checking for this condition and only inspecting the status field, which is of course 0 - and is the meaning of