调用Power类Convert方法时Unit属性空引用异常排查求助

我定义了功率单位枚举类PowerUnit（继承自StringEnumeration）：

public sealed record PowerUnit : StringEnumeration
{
    public static readonly PowerUnit BTUH = new(nameof(BTUH), UnitConstants.BritishThermalUnitsPerHour);
    public static readonly PowerUnit WATT = new(nameof(WATT), UnitConstants.Watt);

    private static readonly Dictionary<string, PowerUnit> _byNameDictionary = GetByNameDictionaryInternal<PowerUnit>();
    public static PowerUnit ByName(string name) => _byNameDictionary[name];

    private PowerUnit() { }
    public PowerUnit(string id, string name) : base(id, name) { }

    public static PowerUnit FromUnitsNetUnit(UnitsNet.Units.PowerUnit unitsNetUnit)
        => unitsNetUnit switch
        {
            UnitsNet.Units.PowerUnit.BritishThermalUnitPerHour => BTUH,
            UnitsNet.Units.PowerUnit.Watt => WATT,
            _ => throw new ArgumentException("Invalid unit type.", nameof(unitsNetUnit))
        };

    // The following is internal because if 'public' it causes HC pipeline initialization to crash
    internal UnitsNet.Units.PowerUnit ToUnitsNetUnit()
        => this.Id switch
        {
            nameof(BTUH) => UnitsNet.Units.PowerUnit.BritishThermalUnitPerHour,
            nameof(WATT) => UnitsNet.Units.PowerUnit.Watt,
            _ => throw new InvalidOperationException("The equivalent UnitsNet unit is unknown.")
        };
}

以及继承自抽象类UnitType的Power类：

public class Power : UnitType<Power, PowerUnit>, IConvertibleUnit<Power, PowerUnit>
{
    public Power() { }
    public Power(Power source) : base(source){ }
    public Power(PowerUnit unit, double scalar) : base(unit, scalar) {}

    public override Power Convert(PowerUnit toUnit)
    {
        if (toUnit == this.Unit) return new(this);

        UnitsNet.IQuantity powerQuantity = UnitsNet.Power.From(Scalar, Unit.ToUnitsNetUnit()); // 此处触发异常，Unit为null
        var toScalar = powerQuantity.ToUnit(toUnit.ToUnitsNetUnit()).Value;

        return new(toUnit, toScalar);
    }
}

UnitType抽象类定义如下：

public abstract class UnitType<T0, T1> where T0: class, IConvertibleUnit<T0, T1>
    where T1: StringEnumeration
{
    public string UnitId { get; set; }
    public T1 Unit { get; set; }
    public double Scalar { get; set; }

    protected UnitType() { }
    protected UnitType(UnitType<T0, T1> source)
    {
        UnitId = source.UnitId;
        Unit = source.Unit;
        Scalar = source.Scalar;
    }

    protected UnitType(T1 unit, double scalar)
    {
        UnitId = unit.Id;
        Unit = unit;
        Scalar = scalar;
    }

    public abstract T0 Convert(T1 toUnit);
}

我将Power作为Space实体的数据库列类型：

public class Space 
{
    //.....
    public Power ElectricalPowerOverride { get; set; }
   //....       
 }

当通过EF Core从数据库获取Space实体后，执行以下代码时：

var dhSpace = _dbContext.Spaces.SingleOrDefault(space => space.ProjectNumber == _designHubProject.ProjectNumber);
var electricalPowerLevelInSI = dhSpace.ElectricalPowerOverride.Convert(PowerUnit.WATT).Scalar;

Power类Convert方法中的Unit属性为空，调用Unit.ToUnitsNetUnit()触发空引用异常。请问出现此异常的原因是什么？

• EF Core加载实体时，会使用Power的无参构造函数创建实例，而无参构造函数调用基类UnitType的无参构造后，Unit属性只会被初始化为null，不会自动关联对应的PowerUnit枚举实例。
• 数据库中存储的是UnitId字段，EF Core仅会为UnitId赋值，但没有内置逻辑将UnitId转换为对应的PowerUnit实例并赋值给Unit属性。因此从数据库加载后的Power对象，只有UnitId和Scalar有值，Unit属性保持null状态。
• Convert方法直接依赖Unit属性调用ToUnitsNetUnit()，未从UnitId重新获取对应的PowerUnit实例，最终触发空引用异常。

内容的提问来源于stack exchange，提问作者Glory Raj