Minecraft freezes when using the command.

[WaningMatrix]

So whenever I Run the Minecraft Client the client launches successfully but as soon as I run my command like /command , mc freezes and intelliJ shows this in the debug screen

and the main console shows this

Here is my ProcessCommand 

public void processCommand(ICommandSender sender, String[] args) throws CommandException {
        if (args.length == 0) {
            // do this
        } 
  else if (args[0].equalsIgnoreCase("add")) {
                // do this
        } 
  else if (args[0].equalsIgnoreCase("remove")) {
                // do this
        } 
  else if (args[0].equalsIgnoreCase("list")) {
                // do this
         }
  else if (args[0].equalsIgnoreCase("flush")) {
                //do this
        } 
  else  {
                sender.addChatMessage(new ChatComponentText(EnumChatFormatting.RED + "Error: Wrong command usage"));
        }
}

What am I doing wrong in here?