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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 make_filter_string(cls, filter_specification):
 """ Converts the given filter specification to a CQL filter expression. """

        registry = get_current_registry()
        visitor_cls = registry.getUtility(IFilterSpecificationVisitor,
                                          name=EXPRESSION_KINDS.CQL)
        visitor = visitor_cls()
        filter_specification.accept(visitor)
        return str(visitor.expression)