Invalid memory address or nil pointer dereference error

Hi
The code based on the release of v20.07.0 .

I modified the code to fix some bugs .
for example:
Bulk loader crashes during reduce phase - #26 by BlankRain
The git log ,I based is this one.

commit 7431be0dce0ffc42e3ff3e31b39fcdd5505e2bb3
Author: Martin Martinez Rivera <martinmr@dgraph.io>
Date:   Mon Aug 3 11:54:25 2020 -0700

    add cluster lables to the jaeger containers (#5951) (#6009)