Find ATH and ATL

hey guys im trying to get all time high and all time low, but the second one return always a zero? why? is based on low. i leave a pic of the code

Not sure why either
Try this way

// function to get all-time high
get_all_time_high() =>
    h = 0.0
    h := barstate.isfirst ? high : high > h[1] ? high : h[1]
    h

// function to get all-time low    
get_all_time_low() =>
    l = 0.0
    l := barstate.isfirst ? low : low < l[1] ? low : l[1]
    l    

// getting all-time high/low    
h0 = security(syminfo.tickerid, 'M', get_all_time_high())
l0 = security(syminfo.tickerid, 'M', get_all_time_low())

// plotting
plot(h0, offset=-9999999, color = color.blue, trackprice=true, linewidth=3)
plot(l0, offset=-9999999, color = color.blue,  trackprice=true, linewidth=3)