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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _validate_names(names):
 """ 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. """


    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