code: public Command redoNext() {
          Command nextCommand;
          if (redoStack.size() > 0) {
              nextCommand = redoStack.pop();
          } else {
              // redo the last command that was done
              nextCommand = undoStack.pop();
              // put it again on the stack
              undoStack.push(nextCommand);
          }
          undoStack.push(nextCommand);
          nextCommand.redo();
          return nextCommand;
      }
docs: Pops the last command from the redo stack, puts it on the com.github.vatbub.common.core.undo stack and calls its {@link Command#redo()}-method. If no command is found on the redo stack,the last command from the undo stack is redone.
  
  @return The command that was redone. <b>Its redo method was already called!</b>