In a fillable Adobe form,  I need a required field to accept 0 as an acceptable answer.

I have a form that asks the following:

Number of grades of gasoline:  _________
Number of grades of diesel:     __________

Both fields are set as required, but zero is an acceptable answer for one or the other.  When the user completes one or the other with 0 and then tries to apply their electronic signature, Adobe responds that a required field has not been completed.  If you change the 0 to a 1, the form will then accept the signature (i.e. the required field requirements are met).  Changing the validate setting to accept values from 0 - 99 did not help.