[TypeScript] Mistakes Map.get() to potentially return undefined

[beefchimi]

Within socialite.ts, we have the following code:

const targetNetwork = id && this.hasNetwork(id) ? this._networks.get(id) : this.getNetworkFromDomain(matches.domain);

TypeScript seems to think its possible for this._networks.get(id) to return undefined, even though it is qualified by id && this.hasNetwork(id). Ideally, we have a way of asserting that the network exists when that condition is reached.