code: def _validate_annotations(annotations, label, add_error):
      
      if annotations is None:
          return
      if not isdict(annotations):
          add_error('{} has invalid annotations {}'.format(label, annotations))
          return
      # Check that all the annotations keys are strings.
      if not all(map(isstring, annotations)):
          add_error(
              '{} has invalid annotations: keys must be strings'.format(label))
docs: Check that the given service or machine annotations are valid.
  
      Use the given label (e.g. "machine X" or "service Y") to describe
      possible errors.
      Use the given add_error callable to register validation error.