code: def is_null(*symbols):
      
      from symbols.symbol_ import Symbol
  
      for sym in symbols:
          if sym is None:
              continue
          if not isinstance(sym, Symbol):
              return False
          if sym.token == 'NOP':
              continue
          if sym.token == 'BLOCK':
              if not is_null(*sym.children):
                  return False
              continue
          return False
      return True
docs: True if no nodes or all the given nodes are either
      None, NOP or empty blocks. For blocks this applies recursively