code: def _validate_names(names):
      
  
      if names is not None:
          if len(names) != len(set(names)):
              msg = ("Duplicate names specified. This "
                     "will raise an error in the future.")
              warnings.warn(msg, UserWarning, stacklevel=3)
  
      return names
docs: Check if the `names` parameter contains duplicates.
  
      If duplicates are found, we issue a warning before returning.
  
      Parameters
      ----------
      names : array-like or None
          An array containing a list of the names used for the output DataFrame.
  
      Returns
      -------
      names : array-like or None
          The original `names` parameter.