Null check on configuration before adding listener fix #164

Author: oliemansm

src/main/java/graphql/servlet/AbstractGraphQLHttpServlet.java

@@ -13,7 +13,11 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import javax.servlet.*;
+import javax.servlet.AsyncContext;
+import javax.servlet.AsyncEvent;
+import javax.servlet.AsyncListener;
+import javax.servlet.Servlet;
+import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -264,11 +268,19 @@ private void mapMultipartVariables(GraphQLRequest request,
     }
 
     public void addListener(GraphQLServletListener servletListener) {
-        configuration.add(servletListener);
+        if (configuration != null) {
+            configuration.add(servletListener);
+        } else {
+            listeners.add(servletListener);
+        }
     }
 
     public void removeListener(GraphQLServletListener servletListener) {
-        configuration.remove(servletListener);
+        if (configuration != null) {
+            configuration.remove(servletListener);
+        } else {
+            listeners.remove(servletListener);
+        }
     }
 
     @Override
@@ -454,23 +466,28 @@ default void accept(HttpServletRequest request, HttpServletResponse response) {
 
     private static class SubscriptionAsyncListener implements AsyncListener {
         private final AtomicReference<Subscription> subscriptionRef;
+
         public SubscriptionAsyncListener(AtomicReference<Subscription> subscriptionRef) {
             this.subscriptionRef = subscriptionRef;
         }
 
-        @Override public void onComplete(AsyncEvent event) {
+        @Override
+        public void onComplete(AsyncEvent event) {
             subscriptionRef.get().cancel();
         }
 
-        @Override public void onTimeout(AsyncEvent event) {
+        @Override
+        public void onTimeout(AsyncEvent event) {
             subscriptionRef.get().cancel();
         }
 
-        @Override public void onError(AsyncEvent event) {
+        @Override
+        public void onError(AsyncEvent event) {
             subscriptionRef.get().cancel();
         }
 
-        @Override public void onStartAsync(AsyncEvent event) {
+        @Override
+        public void onStartAsync(AsyncEvent event) {
         }
     }