code: @Override
  	public void accept(Visitor<Operator<?>> visitor) {
  		if (visitor.preVisit(this)) {
  			this.input.accept(visitor);
  			for (Operator<?> c : this.broadcastInputs.values()) {
  				c.accept(visitor);
  			}
  			visitor.postVisit(this);
  		}
  	}
docs: Accepts the visitor and applies it this instance. The visitors pre-visit method is called and, if returning
  <tt>true</tt>, the visitor is recursively applied on the single input. After the recursion returned,
  the post-visit method is called.
  
  @param visitor The visitor.
  
  @see org.apache.flink.util.Visitable#accept(org.apache.flink.util.Visitor)