Use NULL instead of 0 for pointers.

fgetln(3) will returns NULL if cannot get a line from a stream.
strsep(3) it will returns NULL if the end of the string was reached.
jemalloc(3) malloc will returns NULL if it cannot allocate memory.
fgetln(3) it will returns NULL if it cannot get a line from a stream.

MFC after: 4 weeks