base - how to test if numerical field on a form is empty

Hi,

How to properly test if a numerical field on a form is empty?

I’ve tried a few options, first with a newly initialized form. Then I entered a value in the textbox and deleted it immediately. Then I ran the test a second time.

isNull

if isNull(oNumericalBox.value) then
	msgbox "isNull true, value= " & oNumericalBox.Value
else
	msgbox "isNull false, value= " & Cstr(oNumericalBox.Value) 'Cstr used to avoid an error
endif

'--> output 1st time: isNull false, value= 
'--> output 2nd time: isNull false, value= 0

isEmpty

if isEmpty(oNumericalBox.value) then
	msgbox "isEmpty true, value= " & oNumericalBox.Value
else
	msgbox "isEmpty false, value= " & oNumericalBox.Value
endif

'--> output 1st time: isEmpty true, value= 
'--> output 2nd time: isEmpty false, value= 0

= 0

if oNumericalBox.value = 0 then
	msgbox "= 0 true, value= " & oNumericalBox.Value
else
	msgbox "= 0 false, value= " & oNumericalBox.Value
endif

'--> output 1st time: = 0 true, value= 
'--> output 2nd time: = 0 true, value= 0

It seems these three tests cannot be used to detect an empty numerical textbox or to differentiate between an empty textbox or a textbox with value = 0.

So what should I use instead?

tnx

ps using LO 6.2.8.2 (downloaded from the LO website) on Linux Mint 18.3 mate