I setup a formula field adding a number of month to a date field.

The Expression in the formula field ("TermDate") is :

Date.addMonth(Periode)

Where "Date" is a date field in the form and "Periode" is a numeric field in the form

The formula field work great but after a moment, before finishing the input of the record in the form an error message popup tellng :

"Invalid value found

Field Name : TermDate"

Anyone to explain me what I did wrong ?