Fixes protocol value checking before converting to string

[cantidio]

fixes #359

[hyperlink]

this can be written as:

if (value != null) {

[estliberitas]

LGTM except minor nit described by @hyperlink

[cantidio]

@estliberitas @hyperlink I would agree with this, but sometimes this type of abstraction is not very good.
For instance all comparisons on the project are made using strict checking with '==='. Then we start introducing abstract checking it makes things confusing.

For instance you can open the same file in the future for a refactor and think that this '==' is a mistake and change it back to '==='. Tests could help preventing this, but that's my only concern. Linters would complain about abstract checking as well.

It's more of a question of abstract vs strict checking.

But up to you guys, I can change it if you really thing that my point doesn't make sense. :)