You are using the ProvincialEntity instance as the key, and your ProvincialEntity class does not have a customized toString() method, so you use the default toString() method and convert it into the form of package name.class name@hash code, This is wrong. You are effectively exposing your background details to the client.
When parsed by the client:
{} represents an object context:
Suppose var x = {a : 'b'}
x.a ===> 'b'
or x['a'] ===> 'b'