Fix the case when the callback provided to the client is NULL.
Fix the case when the callback provided to the client is NULL.

nightrune/ola,ld3300/ola,ld3300/ola,ld3300/ola,nightrune/ola,ld3300/ola,nightrune/ola,ld3300/ola,nightrune/ola,nightrune/ola,ld3300/ola,nightrune/ola,nightrune/ola,ld3300/ola