Merge BoolOp operand type.

        BoolOp are "and" and "or" and may return any of these results so all
        operands should have the combinable type.

def visit_BoolOp(self, node):
        """
        Merge BoolOp operand type.

        BoolOp are "and" and "or" and may return any of these results so all
        operands should have the combinable type.
        """
        # Visit subnodes
        self.generic_visit(node)
        # Merge all operands types.
        [self.combine(node, value) for value in node.values]