[1.15.2] MultiPartBlockStateBuilder doesn't synthesize a valid blockstate file when 'useOr' is included in the definition

When using MultiPartBlockStateBuilder to synthesize blockstate JSON files using the 'useOr()' method, the resulting JSON doesn't conform to the required blockstate format.

Attempting to load the synthesized file returns:

'Mod Resources': Expected OR to be a JsonArray, was an object ({"no...e"})

For example:

builder.part().modelFile(model).addModel().useOr().condition(MyBlock.NORTH, true).condition(MyBlock.SOUTH, true);

produces:

{
"multipart": [
  {
    "when": {
       "OR": {
          "north": true,
          "south": true
          },
    "apply": {
      "model": "mymod:block/my_block"
    }
  }
}

but it should produce:

{
"multipart": [
  {
    "when": {
       "OR": [
          { "north": true },
          { "south": true }
          ]
    },
    "apply": {
      "model": "mymod:block/my_block"
    }
  }
}

Looking at the code, there doesn't seem to be any way to force the JSON builder to render the condition as an array of maps instead of a single map.