code: public InstagramSubscription radius(String radius){
  		Preconditions.checkValidRadius(radius, "Invalid 'radius' key");
  		
  		this.params.put(Constants.RADIUS, radius);
  		
  		return this;
  	}
docs: Configure the radius for geography subscription
  @param radius The radius for geography subscription in metre
  @return the {@link InstagramSubscription} instance for method chaining