Nop version 4.6(String Validation Issue)

I try to store empty string, then I get validation error (ex. The Test field is required.)
I didn't do anything for required fields(like code, [required] in model)
In old nopcommerce version possible to store empty string value......................

Please provide more information.  Where do you see the message?  What is a "Test field"?
Is this related to your customization?

Make the field nullabel in the model

        [NopResourceDisplayName("Plugins.Group.Name.Fields.TestField")]
        public string? TestField{ get; set; }

Dear Sir,
I'm not going to tell you how to fix it, but in previous NopCommerce versions without ("Make the field nullable in the model"), I was saving nullable string.
because it is possible to store empty and null values in string.