What part of assembly (FASM) produces null-byte

See more:

ASM

FASM

I made a simple shellcode and tried to disassemble it with IDA Free version and I got this:
IDA view tab
IDA Hex-view tab
note: I can't upload my own, I just find something in the web :(
May I ask where do I get my shellcode? shall I get it on the "Hex-view" or "IDA view" tab?

but if you don't mind I would like to ask for some reference where I can know if what syntax (the "mov","push","pop",etc... I don't know what's it called) of FASM are producing null-bytes? I would like to avoid them :)

What I have tried:

I tried analyzing the disassembled file :)