[Fix] Fix bug with missing license information

[sorenlouv]

I thought that license information would always include something like:

{
  features: {
    watcher: { isAvailable: false },
    ml: { isAvailable: false }
  }
}

Turns out we can't rely on this being available, so have to guard the accessors with lodash.

TODO:

• Add tests

[elasticmachine]

Pinging @elastic/apm-ui

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[jasonrhodes]

Looks good -- any reason not to do
get(license, 'data.some.path') instead of get(license.data, 'some.path') in these cases?

[sorenlouv]

I try to avoid _.get when a values is guaranteed to be available - and if it isn't available, it points to a bug somewhere else in the system. Using _.get can sometimes hide these bugs.

When I do use _.get I try to do it only for the part that is not guaranteed. In this case I know that license.data is guaranteed to be declared (might be undefined):

https://github.com/elastic/kibana/blob/master/x-pack/plugins/apm/public/store/reactReduxRequest/helpers.js#L14-L17

That's at least the reasoning I tell myself :)

[jasonrhodes]

@sqren yeah this makes sense with null pointer bugs and all that, I think at some point I changed my mind on this a bit in some cases where I know I want to avoid bubbling that error up to the user in either case. Being able to log something about the unexpected undefined value would be a nice middle ground but I don't know that we have a good way to do that.

Out of curiosity: would an ErrorBoundary have let us show a more useful screen when that value was undefined/blew up? We used them a bit but I was always a little fuzzy on how they work tbh.

[sorenlouv]

I think at some point I changed my mind on this a bit in some cases where I know I want to avoid bubbling that error up to the user in either case.

What I'm hoping is that the error will never make it to the user, since it'll be obvious in dev-mode when everything explodes - but that also sounds like a dangerous way to code, when I put it like that, so I'm on the fence :)

I haven't really used ErrorBoundaries yet but they sound useful.