EnumSpeed_04

    public static class InvoicePaymentMethodExtensions
    {
        public static bool IsUndefined_WithEnumIsDefined(this InvoicePaymentMethod paymentMethod)
        {
            if (paymentMethod == InvoicePaymentMethod.Undefined)
            {
                return true;
            }

            var isDefined = Enum.IsDefined(typeof(InvoicePaymentMethod), paymentMethod);
            return !isDefined;
        }

        public static bool IsUndefined_WithComparingAllValidValuesDirectly(this InvoicePaymentMethod paymentMethod)
        {
            if (paymentMethod == InvoicePaymentMethod.Undefined)
            {
                return true;
            }

            return
                paymentMethod != InvoicePaymentMethod.AutoGiroNorway &&
                paymentMethod != InvoicePaymentMethod.Collection &&
                paymentMethod != InvoicePaymentMethod.Common &&
                paymentMethod != InvoicePaymentMethod.Combined &&
                paymentMethod != InvoicePaymentMethod.PrePaid &&
                paymentMethod != InvoicePaymentMethod.Compensation &&
                paymentMethod != InvoicePaymentMethod.AvtaleGiro &&
                paymentMethod != InvoicePaymentMethod.AvtaleGiroSent &&
                paymentMethod != InvoicePaymentMethod.AvtaleGiroSentNoMsg &&
                paymentMethod != InvoicePaymentMethod.AvtaleGiroDeleted &&
                paymentMethod != InvoicePaymentMethod.AvtaleGiroOcr &&
                paymentMethod != InvoicePaymentMethod.ManualPrint &&
                paymentMethod != InvoicePaymentMethod.SmallAmount &&
                paymentMethod != InvoicePaymentMethod.Salary &&
                paymentMethod != InvoicePaymentMethod.Banker &&
                paymentMethod != InvoicePaymentMethod.Order &&
                paymentMethod != InvoicePaymentMethod.Invoice &&
                paymentMethod != InvoicePaymentMethod.ChequeAgent &&
                paymentMethod != InvoicePaymentMethod.DebtInsuranceClaim;
        }

        private static HashSet<InvoicePaymentMethod> _allDefinedValues;
        static InvoicePaymentMethodExtensions()
        {
            _allDefinedValues = new HashSet<InvoicePaymentMethod>(Enum.GetValues(typeof(InvoicePaymentMethod)).Cast<InvoicePaymentMethod>());
        }

        public static bool IsUndefined_WithHashSet(this InvoicePaymentMethod paymentMethod)
        {
            if (paymentMethod == InvoicePaymentMethod.Undefined)
            {
                return true;
            }

            return !_allDefinedValues.Contains(paymentMethod);
        }
    }