How to set the estimated Budget to 0 or to "nothing"

[crouser7]

Hello there,

i a creating a function that checks if the estimated budget is within the planned budget.
For not fully planned projects i write the remaining free budget in a special issue.
When the Budget and plan is met perfectly i want to write 0 and see 0 in that special issue.
For overplanned Projects i cannot write -50 into the Budget as this is not allowed by redmine, but i want to set it to empty.

What i have found so far, Whether i write 0 as a float or Null into the estimated budget for the special issue, makes the Display show nothing.
I found a workaround by writing 0.0000001 into the estimated budget to show 0, but thats a little too dirty for me.
Is there a better way to write 0 into the estimated budget?
When operating in the Webpage i can write 0 and it stays or clear it and it is cleared.