This looks to be working…
# Get default value
set dflt [TioGetDefault 1]
set passThru [TioGetPassThrough 1]
# If the value does not exist, Just return default
#if {![TioExists 1 $val $side]} {return $dflt}
if {![TioExists 1 $val $side] && $passThru == 1} {
return $val
} elseif {![TioExists 1 $val $side] && $passThru == 0} {
return $dflt
}