docs: Handle NULL in example
docs: Handle NULL in example

Closes #361

redis/hiredis,redis/hiredis,jinguoli/hiredis,redis/hiredis,owent-contrib/hiredis,charsyam/hiredis,thomaslee/hiredis,jinguoli/hiredis,charsyam/hiredis,thomaslee/hiredis,jinguoli/hiredis,owent-contrib/hiredis