Bot framework crash deserializing empty string with iPhone payload

I have an adaptive card my bot put into a chat. The card includes a button which results in an invoke action being called. This works fine on desktop, web and android. But crashes on iphone. The issue appears to be that on iphone an empty 'tabContext' dict element is set with the value being an empty string and the bot framework crashes calling a .get on an empty string.

Here is the payload:

"value": {
  "context": {
    "theme": "default"
  },
  "data": {
    "fetch_id": 6,
    "type": "task/fetch",

  },
  "tabContext": ""
},

I assume this is a bug in the iphone Teams client but wanted to check if anyone else had encountered this?

Stacktrace:

File "msrest/serialization.py", line 1162 in, rest_key_extractor
    return working_data.get(key)
AttributeError: 'str' object has no attribute 'get'