doc: recommend optional pointers for nullptrs instead of allowzero
doc: recommend optional pointers for nullptrs instead of allowzero

raulgrell/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig