If a Milestone has one or more Vendors that are relevant to it, this will contain information about that vendor that you can choose to show.
Type: object
Object Properties
Mapped to Definition
The hash identifier of the Vendor related to this Milestone. You can show useful things from this, such as thier Faction icon or whatever you might care about.
Type: uint32
Mapped to Manifest Database Definition: Destiny.Definitions.DestinyVendorDefinition
Nullable Mapped to Definition
If this vendor is featuring a specific item for this event, this will be the hash identifier of that item. I'm taking bets now on how long we go before this needs to be a list or some other, more complex representation instead and I deprecate this too. I'm going to go with 5 months. Calling it now, 2017-09-14 at 9:46pm PST.
Type: uint32
Mapped to Manifest Database Definition: Destiny.Definitions.DestinyInventoryItemDefinition