[BUG] Cannot coerce empty Array[File] to Array[String]?

[jebob]

I think the minimum to reproduce the bug is just

  Array[File] foo = []
  Array[String]? bar = foo

which fails with

  "failures": [
    {
      "causedBy": [
        {
          "message": "Failed to evaluate 'bar' (reason 1 of 1): Evaluating foo failed: assertion failed: base member type WomMaybeEmptyArrayType(WomStringType) and womtype WomMaybeEmptyArrayType(WomSingleFileType) are not compatible",
          "causedBy": []
        }
      ],
      "message": "Workflow failed"
    }
  ],

Interestingly enough, this passes if the array is non-empty, or if the target is not optional, or if the source is type Array[String].

I am running cromwell "v85 (ish)" according to the administrator. Backend is AWS batch.