48. Safe MUX

How do you plan to solve it?

module safe_mux2 (input [7:0] a, input [7:0] b, input sel, output reg [7:0] y, output reg sel_unknown);
    always @* begin
        y = 8'h00; sel_unknown = 1'b0;
        if (sel === 1'b0) begin
            y = a;
        end else if (sel === 1'b1) begin
            y = b;
        end else begin
            sel_unknown = 1'b1; y = 8'h00;
        end
    end
endmodule