code: public function push($middleware)
      {
          if (is_array($middleware)) {
              $this->stack = array_merge($this->stack, $middleware);
  
              return $this;
          }
  
          $this->stack[] = $middleware;
  
          return $this;
      }
docs: Adds a new middleware or a list of middlewares in the stack.
  
  @param  \Closure|array|object|string $middleware
  @return self