Calculated Column logic

lets say you have a date column date1
you can have logic as follows

if(columna = "hello",Today(),"")

this should really fail because "" is not a date
it doesn't fail, but access for example will come up with #error

 lets say I want to keep the null



if(columna = "hello",Today(),date1)

this fails because of circular logic

if(columna = "hello",Today(),null)
if(columna = "hello",Today(),blank)

these are also not correct syntax

if(columna = "hello",Today())

that works but updates the column with a 0 which SharePoint shows incredibly as a 0