(#51) add "omitempty" option to nilable fields

[blukai]

I faced the problem that is described in #51 and after short investigation came up with this solution.
please let me know if tests needs to be added, etc.

closes #51

[Yamashou]

please tell me the result of generating code. I want to see that.

[blukai]

example repo with two branches with-omitempty and without-omitempty:
https://github.com/blukai/gqlgenc-omitempty-example

here's the diff blukai/gqlgenc-omitempty-example@cec3d5a

[Yamashou]

LGTM!

I will merge as soon as I can confirm that the generated code is correct!

[mlaflamm]

This is exactly what I need. I would love to see this merged.

[mlaflamm]

Shouldn't omitempty only present on input structs?

[Yamashou]

Shouldn't omitempty only present on input structs?

@mlaflamm
So sorry, I have so many work. your opinion is a correct. Should I fix that ?

[Yamashou]

@mlaflamm
your saying is other PR. please waiting soon!

[mlaflamm]

Thank you for merging this.

I don't think that having omitempty everywhere has any negative impacts other than potentially mislead someone reading the generated code as thinking this is useful for non input structs. IMHO, having omitempty only on input is a low priority change.