code: def link_is_valid_relative(link, base_dir):
      if link is None:
          return True
  
      if os.path.isabs(link):
          # absolute links aren't allowed
          return False
  
      if link.lower().startswith("http"):
          # github (and other website) links aren't allowed either
          return False
  
      return os.path.exists(os.path.join(base_dir, link))
  
imports: import abc
  import argparse
  import contextlib
  import difflib
  import enum
  import glob
  import itertools
  import json
  import nbformat
  import os.path
  import re
  import subprocess
  import sys
  import textwrap
label_desc: Use image node_id 2 for calling a global function with example usage: link_is_valid_relative(link, base_dir) and returns: os, True, False, False