class_docstr: NNI tuners/assessors/adivisors accept a `classArgs` parameter in experiment configuration file.
  This ClassArgsValidator interface is used to validate the classArgs section in exeperiment
  configuration file.
code: def path(self, key):
      return And(
          And(str, error="%s should be a string!" % key),
          And(
              lambda p: Path(p).exists(),
              error="%s path does not exist!" % (key),
          ),
      )
  
imports: import copy
  from enum import Enum, unique
  from pathlib import Path
  from schema import And
  from .None import parameter_expressions
label_desc: Use image node_id 4 for calling the ClassArgsValidator obj's underlying member method code with example usage: obj.path(key) and returns: And