Concurrenthashmap instead of null check

Author: steviemo

lib/src/main/java/ua/naiksoftware/stomp/client/StompClient.java

@@ -11,6 +11,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 import io.reactivex.BackpressureStrategy;
@@ -33,7 +34,7 @@ public class StompClient {
     public static final String DEFAULT_ACK = "auto";
 
     private Disposable mMessagesDisposable;
-    private Map<String, Set<FlowableEmitter<? super StompMessage>>> mEmitters = new HashMap<>();
+    private Map<String, Set<FlowableEmitter<? super StompMessage>>> mEmitters = new ConcurrentHashMap<>();
     private List<ConnectableFlowable<Void>> mWaitConnectionFlowables;
     private final ConnectionProvider mConnectionProvider;
     private HashMap<String, String> mTopics;
@@ -177,16 +178,14 @@ public Flowable<StompMessage> topic(String destinationPath, List<StompHeader> he
                while (mapIterator.hasNext()) {
                    String destinationUrl = mapIterator.next();
                    Set<FlowableEmitter<? super StompMessage>> set = mEmitters.get(destinationUrl);
-                   if (null != set) {
-                       Iterator<FlowableEmitter<? super StompMessage>> setIterator = set.iterator();
-                       while (setIterator.hasNext()) {
-                           FlowableEmitter<? super StompMessage> subscriber = setIterator.next();
-                           if (subscriber.isCancelled()) {
-                               setIterator.remove();
-                               if (set.size() < 1) {
-                                   mapIterator.remove();
-                                   unsubscribePath(destinationUrl).subscribe();
-                               }
+                   Iterator<FlowableEmitter<? super StompMessage>> setIterator = set.iterator();
+                   while (setIterator.hasNext()) {
+                       FlowableEmitter<? super StompMessage> subscriber = setIterator.next();
+                       if (subscriber.isCancelled()) {
+                           setIterator.remove();
+                           if (set.size() < 1) {
+                               mapIterator.remove();
+                               unsubscribePath(destinationUrl).subscribe();
                            }
                        }
                    }