public sealed class ContingentNullValue : ContingentValue 

public void ExploreContingentValues(Table table)
{
    using (TableDefinition tableDefinition = table.GetDefinition())
    {
        IReadOnlyList<Contingency> contingencies = tableDefinition.GetContingencies();
        foreach (Contingency contingency in contingencies)
        {
            // Field group 
            FieldGroup filedGroup = contingency.FieldGroup;
            string fieldGroupName = filedGroup.Name;
            IReadOnlyList<string> fieldInFieldGroup = filedGroup.FieldNames;
            bool isEditRestriction = filedGroup.IsRestrictive;

            int contingencyId = contingency.ID;
            Subtype subtype = contingency.Subtype;
            bool isContingencyRetired = contingency.IsRetired;

            // Contingent values 
            IReadOnlyDictionary<string, ContingentValue> contingentValuesByFieldName = contingency.GetContingentValues();
            foreach (KeyValuePair<string, ContingentValue> contingentValueKeyValuePair in contingentValuesByFieldName)
            {
                string attributeFieldName = contingentValueKeyValuePair.Key;

                // Contingent value type associated with the attribute field
                ContingentValue contingentValue = contingentValueKeyValuePair.Value;

                switch (contingentValue)
                {
                    case ContingentCodedValue contingentCodedValue:
                        string codedValueDomainName = contingentCodedValue.Name;
                        object codedValueDomainValue = contingentCodedValue.CodedValue;
                        break;
                    case ContingentRangeValue contingentRangeValue:
                        object rangeDomainMaxValue = contingentRangeValue.Max;
                        object rangeDomainMinValue = contingentRangeValue.Min;
                        break;
                    case ContingentAnyValue contingentAnyValue:
                        // Any value type
                        break;
                    case ContingentNullValue contingentNullValue:
                        // Null value
                        break;
                }
            }
        }
    }
}

public void GetPossibleContingentValues(FeatureClass parcels, string zoningFieldName = "Zone")
{
    using (RowBuffer rowBuffer = parcels.CreateRowBuffer())
    {
        IReadOnlyDictionary<FieldGroup, IReadOnlyList<ContingentValue>> possibleZonings = parcels.GetContingentValues(rowBuffer, zoningFieldName);
        IEnumerable<FieldGroup> possibleFieldGroups = possibleZonings.Keys;
        foreach (FieldGroup possibleFieldGroup in possibleFieldGroups)
        {
            IReadOnlyList<ContingentValue> possibleZoningValues = possibleZonings[possibleFieldGroup];
            foreach (ContingentValue possibleZoningValue in possibleZoningValues)
            {
                switch (possibleZoningValue)
                {
                    case ContingentCodedValue codedValue:
                        string codedValueDomainName = codedValue.Name;
                        object codedValueDomainValue = codedValue.CodedValue;
                        break;
                    case ContingentRangeValue rangeValue:
                        object rangeDomainMaxValue = rangeValue.Max;
                        object rangeDomainMinValue = rangeValue.Min;
                        break;
                    case ContingentAnyValue contingentAnyValue:
                        // Any value type
                        break;
                    case ContingentNullValue contingentNullValue:
                        // Null value
                        break;
                }
            }
        }
    }
}