make sure the context exists before attempting to access its properties

[jfstgermain]

[TheBenji]

Can we merge this? This would be a great addition for us too!

[guyguyon]

@TheBenji I wonder if we want to throw exception in that case

[TheBenji]

A clear exception would be fine but intuitively I'd expect it to return undefined just the same as if I hadn't set the key in the first place I guess

[guyguyon]

I meant to throw exception in case you don't have executionAsyncId

if (this.context[eid]) {
     this.context[eid][key] = val;
} else {
   throw ....
}

[eladchen]

Any reason for this PR to remain stale..?

[guyguyon]

@eladchen Yes. I've asked about throwing an exception, and there is a conflict to resolve