Using Experimental Mirrors Based Approach, getting exception: Class '_LocalInstanceMirrorImpl' has no instance method 'then'.

[proteme]

Thanks for this valuable effort. I have just started playing with it.

I am using the following code as suggested by the documentation:

objectToJson(instanceOfMyClass).then((jsonStr) => print(jsonStr));

However, I get the exception:
Breaking on exception: Class '_LocalInstanceMirrorImpl' has no instance method 'then'.