fix potential NPE and repeated conditional test (#5776)

### Motivation

fix potential NPE and repeated conditional test

### Modifications

local changes

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ClientCnx.java

@@ -308,7 +308,7 @@ public class ClientCnx extends PulsarHandler {
     @Override
     protected void handleAuthChallenge(CommandAuthChallenge authChallenge) {
         checkArgument(authChallenge.hasChallenge());
-        checkArgument(authChallenge.getChallenge().hasAuthData() && authChallenge.getChallenge().hasAuthData());
+        checkArgument(authChallenge.getChallenge().hasAuthData());
 
         // mutual authn. If auth not complete, continue auth; if auth complete, complete connectionFuture.
         try {

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerImpl.java

@@ -947,7 +947,8 @@ public class ProducerImpl<T> extends ProducerBase<T> implements TimerTask, Conne
             }
             return true;
         } else {
-            log.warn("[{}] Failed while casting {} into ByteBufPair", producerName, op.cmd.getClass().getName());
+            log.warn("[{}] Failed while casting {} into ByteBufPair", producerName,
+                    (op.cmd == null ? null : op.cmd.getClass().getName()));
             return false;
         }
     }
@@ -1253,7 +1254,8 @@ public class ProducerImpl<T> extends ProducerBase<T> implements TimerTask, Conne
                 headerFrame.resetReaderIndex();
             }
         } else {
-            log.warn("[{}] Failed while casting {} into ByteBufPair", producerName, op.cmd.getClass().getName());
+            log.warn("[{}] Failed while casting {} into ByteBufPair", producerName,
+                    (op.cmd == null ? null : op.cmd.getClass().getName()));
         }
     }