Making field required at graph level

Hi I am stuck at a very basic requirement, where i have to make this field required at screen level. Below is Original attributes for that field.

Field Name : ExpirationDate

Data Class : PX.Objects.CR.CRQuote

Original Attributes:

     [PXDBDate(BqlField = typeof(Standalone.CRQuote.expirationDate))]
    [PXMassUpdatableField]
    [PXUIField(DisplayName = "Expiration Date", Visibility = PXUIVisibility.SelectorVisible)]

I tried this by using CustomAttribute for both Required and Default :

 [PXMergeAttributes(Method = MergeMethod.Append)]
 [PXCustomizeBaseAttribute(typeof(PXUIFieldAttribute), "Required", true)]
 protected virtual void CRQuote_ExpirationDate_CacheAttached(PXCache cache){}

and

    [PXMergeAttributes(Method = MergeMethod.Append)]
    [PXDefault(PersistingCheck = PXPersistingCheck.NullOrBlank)]
    protected virtual void CRQuote_ExpirationDate_CacheAttached(PXCache cache)
    {

    }

but still the form is allowing blank values. Please note field is a datetime type.

Please help