Entity conditions for advancements triggers which can only be one type no longer allow you do omit the type condition

The following advancement use to work in 1.12.x

{
  "display": {
    "icon": {
      "item": "minecraft:emerald"
    },
    "title": "Trading in the end",
    "description": "Trading in the end"
  },
  "parent": "example:challenges/root",
  "criteria": {
    "trade_in_the_end": {
      "trigger": "minecraft:villager_trade",
      "conditions": {
        "villager": {
          "location": {
            "dimension": "the_end"
          }
        }
      }
    }
  }
}

From the wiki:

The villager the item was purchased from. The 'type' tag is redundant since it will always be "villager".

However in the 1.13 snapshots, the type tag is now required. The above advancement only works if you add the redundant type field:

{
  "display": {
    "icon": {
      "item": "minecraft:emerald"
    },
    "title": "Trading in the end",
    "description": "Trading in the end"
  },
  "parent": "example:challenges/root",
  "criteria": {
    "trade_in_the_end": {
      "trigger": "minecraft:villager_trade",
      "conditions": {
        "villager": {
          "type": "minecraft:villager",
          "location": {
            "dimension": "the_end"
          }
        }
      }
    }
  }
}

This bug seems like it was introduced due to the changes which were made in 1.13 snapshots to the way entities are registered and constructed. It doesn't seem intentional and I haven't seen it documented in the release notes