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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 ReadClientMetadata(self, client_id):
 """Reads the ClientMetadata record for a single client. Args: client_id: A GRR client id string, e.g. "C.ea3b2b71840d6fa7". Returns: An rdfvalues.object.ClientMetadata object. Raises: UnknownClientError: if no client with corresponding id was found. """

    result = self.MultiReadClientMetadata([client_id])
    try:
      return result[client_id]
    except KeyError:
      raise UnknownClientError(client_id)