Specify when input pointers can be NULL

[RReverser]

For example, apparently (according to examples) it’s ok to pass NULL as thisArg and data to napi_get_cb_info if you don’t want to retrieve it, but this is not mentioned in the docs.

Some other places like napi_wrap mention “optional” explicitly for out params, might be a good idea to go through other functions too and explicitly specify when pointer is "optional" or when it must be non-NULL.

[RReverser]

@sampsongao Are you still planning to do this?

[sampsongao]

I am busy with my assignment for school now. I will continue on this maybe next week or so.

[mhdawson]

Submitted - nodejs/node#40821 for reported instance.
Leaving open as we should look for other cases where we can add the optional info.

[mhdawson]

Submitted nodejs/node#41021 to close out the remaining places that needed an update.