{ "error": "Unexpected token u in JSON at position 0" } code example

Example 1: SyntaxError: Unexpected token u in JSON at

That error is normally seen when the value given to JSON.parse is actually undefined. 
So, I would check the code that is trying to parse this - most likely you are not parsing the actual string shown here.

Example 2: unexpected token s in json at position 0

var s = '"something"';
var result = JSON.parse(s);