Custom Mob won't render -- need help with Animation Controller

I created a new mob (cow_fire) using the Vanilla cow files. I made my modifications and everything works great except that I cannot assign an animation controller. When I include the following lines of code in my cow_fire.entity.json file, my new mob does not render (it becomes invisible and so does its spawn egg).

  "animation_controllers": [
    { "flame": "controller.animation.cow_fire.flame" }
  ],

I have a file called cow_fire.animation_controllers.json in the animation_controllers folder of my resource pack. Its contents are as follows (adapted from the blaze mob animation controllers):

{
    "format_version" : "1.10.0",
    "animation_controllers" : {
        "controller.animation.cow_fire.flame" : {
            "initial_state" : "default",
            "states" : {
                "default" : {
                    "transitions" : [
                        {
                            "flaming" : "!query.is_swimming"
                        }
                    ]
                },
                "flaming" : {
                    "particle_effects" : [
                        {
                            "effect" : "charged_flames"
                        }
                    ],
                    "transitions" : [
                        {
                            "default" : "query.is_swimming"
                        }
                    ]
                }
            }
        }
    }
}

(I am trying to have the cow always be on fire except when it is swimming.)

Note that if I remove all transitions and leave just one default state with nothing in it, the mob still won't render. If I remove the animation_controller reference from the 'cow_fire.entity.json' file, the mob renders just fine.

What am I doing wrong?