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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 GetCredential(self, path_spec, identifier):
 """Retrieves a specific credential from the key chain. Args: path_spec (PathSpec):
 path specification. identifier (str):
 credential identifier. Returns: object: credential or None if the credential for the path specification is not set. """

    credentials = self._credentials_per_path_spec.get(path_spec.comparable, {})
    return credentials.get(identifier, None)