Fluent Validation własny walidator

IRuleBuilderExtensions.cs

public static class IRuleBuilderExtensions
{
    public static IRuleBuilderOptions<T, TProperty> Nip<T, TProperty>(this IRuleBuilder<T, TProperty> ruleBuilder)
    {
        return ruleBuilder.SetValidator(new NipValidator());
    }
}

NipValidator.cs

public class NipValidator : PropertyValidator
{
    public NipValidator()
        : base("{PropertyName} ma niepoprawny format NIPu.")
    {
 
    }
 
    protected override bool IsValid(PropertyValidatorContext context)
    {
        var nip = context.PropertyValue as string;
 
        if (nip == null)
        {
            return false;
        }
 
        return NipValidate(nip);
    }
 
    private bool NipValidate(string nip)
    {
        if (nip.Length != 10)
        {
            return false;
        }
 
        return true;
    }
}

UserValidator.cs

RuleFor(u => u.Nip)
    .Nip();