Apply a visitor to all the function expressions
        Args:
            Visitor: slither.visitors
        Returns
            list(): results of the visit

def apply_visitor(self, Visitor):
        """
            Apply a visitor to all the function expressions
        Args:
            Visitor: slither.visitors
        Returns
            list(): results of the visit
        """
        expressions = self.expressions
        v = [Visitor(e).result() for e in expressions]
        return [item for sublist in v for item in sublist]