Only override Activity when non-null (#3)

Implements JDA-Applications#110

Author: Andre601

command/src/main/java/com/jagrosh/jdautilities/command/CommandClientBuilder.java

@@ -274,7 +274,7 @@ public CommandClientBuilder setEmojis(String success, String warning, String err
 
     /**
      * Sets the {@link net.dv8tion.jda.api.entities.Activity Game} to use when the bot is ready.
-     * <br>Can be set to {@code null} for no activity.
+     * <br>Can be set to {@code null} for JDA Utilities to not set it.
      * 
      * @param  activity
      *         The Game to use when the bot is ready

command/src/main/java/com/jagrosh/jdautilities/command/impl/CommandClientImpl.java

@@ -490,8 +490,10 @@ private void onReady(ReadyEvent event)
             return;
         }
         textPrefix = prefix.equals(DEFAULT_PREFIX) ? "@"+event.getJDA().getSelfUser().getName()+" " : prefix;
-        event.getJDA().getPresence().setPresence(status==null ? OnlineStatus.ONLINE : status, 
-                activity ==null ? null : "default".equals(activity.getName()) ? Activity.playing("Type "+textPrefix+helpWord) : activity);
+        
+        if(activity != null) 
+            event.getJDA().getPresence().setPresence(status==null ? OnlineStatus.ONLINE : status, 
+                "default".equals(activity.getName()) ? Activity.playing("Type "+textPrefix+helpWord) : activity);
 
         // Start SettingsManager if necessary
         GuildSettingsManager<?> manager = getSettingsManager();