Property is possibly undefined even after element access/indexed access

[brawaru]

TypeScript Version: 2.3.4

Code

interface IGuildCustomize {
    /**
     * Welcome message
     */
    welcome_msg?:string;
    /**
     * Channel for welcome message
     */
    welcome_msg_channel:string;
}

let cz = JSON.parse(guildRow.customize) as IGuildCustomize;
if (cz["welcome_msg"] && cz["welcome_msg_channel"]) {
   let channel = msg.guild.channels.get(cz["welcome_msg_channel"]);
   if (!channel || channel.type !== "text") {
    return;
   }
   (channel as TextChannel).send(cz["welcome_msg"].replace("{usermention}", `<@${msg.author.id}>`).replace("{username}", escapeDiscordMarkdown(msg.author.username)));
}

Expected behavior: No errors

Actual behavior: Errors that value possibly can be undefined after if check

[brawaru]

Works fine this way:

[DanielRosenwasser]

Looks like a duplicate of #10530.

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.