wunderground in processing - not working

wunderground_notworking.pde

import com.francisli.processing.http.*;

HttpClient client;

void setup() {
  client = new HttpClient(this, "api.wunderground.com");
  client.GET("/api/[api_key]/conditions/q/CA/San_Francisco.json");
}

void responseReceived(HttpRequest request, HttpResponse response) {
  //// check for HTTP 200 success code
  if (response.statusCode == 200) {
    println(response.getContentAsString());
    JSONObject results = response.getContentAsJSONObject();
    
    String locationInfo = results.get("full").stringValue();
    String currentTime = results.get("observation_time").stringValue();
    int tempF = results.get("temp_f").intValue();
    int tempC = results.get("temp_c").intValue();
    
    println(locationInfo);
    println(currentTime);
    println(tempF + "° F");
    println(tempC + "° C");

  }
}

void draw () {
}

Returns NullPointerException:

Exception in thread "Animation Thread" java.lang.NullPointerException
at wunderground.responseReceived(wunderground.java:37)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.francisli.processing.http.HttpClient.pre(HttpClient.java:163)
at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at processing.core.PApplet$RegisteredMethods.handle(Unknown Source)
at processing.core.PApplet$RegisteredMethods.handle(Unknown Source)
at processing.core.PApplet.handleDraw(Unknown Source)
at processing.core.PApplet.run(Unknown Source)
at java.lang.Thread.run(Thread.java:680)