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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(self, value):
 """Validate an RDFValue instance. Args: value: An RDFValue instance or something which may be used to instantiate the correct instance. Raises: TypeValueError: If the value is not a valid RDFValue instance or the required type. Returns: A Valid RDFValue instance. """

    # Allow None as a default.
    if value is None:
      return

    if not isinstance(value, self.rdfclass):
      # Try to coerce the type to the correct rdf_class.
      try:
        return self.rdfclass(value)
      except rdfvalue.InitializeError:
        raise TypeValueError("Value for arg %s should be an %s" %
                             (self.name, self.rdfclass.__name__))

    return value