title: Data provider format not working in amcharts
body: <p>While setting the data to value field in am charts , if i need to set the value field like "value Field": "cities.a" its not working :( any help is appreciated </p>
  
  <p>My data format:
  data Provider": [ {"year": 2003,"cities":{"a": 2.0,"b": 2.5},"countries":{"c": 2.1,"d": 1.2} }, {"year": 2004,"cities":{"a": 2.6,"b": 2.7},"countries":{"c": 2.2,"d": 1.3} }]</p>