If a date field is empty then how can I compare the date from another field

Question

I have form where a user puts in a date but I want to stop the user from inputting a date which is more than the date on the main form if the date is mentioned and the date shoud also be less than the date already on the same form which is the Date From field.

I came up with this valdidation criteria

>=[DateFrom] And IIf([Forms]![FrmPatientInfo]![EndOfTreatment] Is Null,<=Date(),<=[Forms]![FrmPatientInfo]![EndOfTreatment])

It is not letting me put any dates in the field.

Please tell me what I am doing wrong here.

Answer 1

Try with:

>=[DateFrom] And <=Nz([Forms]![FrmPatientInfo]![EndOfTreatment],Date())

or simply:

>=[DateFrom] And <=Nz([EndOfTreatment],Date())