取消對FirstOrDefault上可能為空的參考的參考

我環顧了各種相關問題，但似乎找不到一個可以幫助我解決這個問題的問題。

我使用 EF Core Power Tools 來設定我的 DbContext；一個具體物體如下：

// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>
#nullable disable
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;

namespace FIS2DataTables.Tables
{
    [Table("Settings", Schema = "static")]
    [Index(nameof(Setting), IsUnique = true)]
    public partial class Settings
    {
        [Key]
        [Column("id")]
        public int Id { get; set; }
        [Required]
        [Column("setting")]
        [StringLength(50)]
        public string Setting { get; set; }
        [Required]
        [Column("value")]
        [StringLength(200)]
        public string Value { get; set; }
        [Column("intValue")]
        public int? IntValue { get; set; }
        [Column("bitValue")]
        public bool? BitValue { get; set; }
    }
}

現在我有兩個不同的檔案參考了這個特定的物體。這是這些檔案之一（簡化）：

using FIS2DataTables.Context;
using FIS2DataTools.Interfaces;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;

namespace FIS2DataTools.Services
{
    public class SettingsService : ISettingsService
    {
        private readonly IConfiguration Configuration;
        private readonly IDbContextFactory<FIS2TableContext> ContextFactory;

        public SettingsService(IDbContextFactory<FIS2TableContext> contextFactory, IConfiguration configuration)
        {
            ContextFactory = contextFactory;
            Configuration = configuration;
        }

        private T GetConfigSetting<T>(string toFind)
        {

            return Configuration.GetValue<T>(toFind);
        }

        private string GetDbSetting(string toFind)
        {
            using (FIS2TableContext context = ContextFactory.CreateDbContext())
            {
                return context.Settings.FirstOrDefault(x => x.Setting == toFind).Value;
            }
        }

        private async Task<string> GetDbSettingAsync(string toFind)
        {
            using (FIS2TableContext context = ContextFactory.CreateDbContext())
            {
                return (await context.Settings.FirstOrDefaultAsync(x => x.Setting == toFind)).Value;
            }
        }

        public string GetDomainName()
        {
            return GetDbSetting("DomainName");
        }

        public string GetPhotosPath()
        {
            return GetDbSetting("PhotosPath");
        }

        public async Task<string> GetPhotosPathAsync()
        {
            return await GetDbSettingAsync("PhotosPath");
        }

        public string GetStoragePath()
        {
            return GetConfigSetting<string>("StoragePaths:Local");
        }
    }
}

有問題的方法是GetDbSetting和它的異步對應方法。在這兩種方法中，此塊：context.Settings.FirstOrDefault(x => x.Setting == toFind)標記為：

取消參考可能為空的參考

我的挖掘基本上說這只是編譯器的說法：

這可能，也許，在某些時候是空的......我不確定

但是......我在解決方案的其他地方有完全相同的代碼（我正在將它從專案 A 遷移到 B 的中途），并且在其他位置它沒有標記它。

First and foremost, I'm surprised by the inconsistency of it; but moreover, I'm wondering what the best course of action to avoid this is?

EDIT: now that I've asked the question; I've realised the instance that gets flagged, is the one where I'm referencing it in a seperate project - it's not as simple as it being that tying the analyser in knots?

For reference, the the other file (the one where it doesn't get flagged) is as follows:

using FIS2DataLibrary.Data.Interfaces;
using FIS2DataLibrary.Helpers;
using FIS2DataLibrary.Tables;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using System.Linq;
using System.Threading.Tasks;

namespace FIS2DataLibrary.Data.Services
{
    public class SettingsService : ISettingsService
    {
        private readonly IConfiguration Configuration;
        private readonly IDbContextFactory<FIS2_TableContext> ContextFactory;

        public SettingsService(IDbContextFactory<FIS2_TableContext> contextFactory, IConfiguration configuration)
        {
            ContextFactory = contextFactory;
            Configuration = configuration;
        }

        private T GetConfigSetting<T>(string toFind)
        {
            return Configuration.GetValue<T>(toFind);
        }

        private string GetDbSetting(string toFind)
        {
            using (FIS2_TableContext context = ContextFactory.CreateDbContext())
            {
                return context.Settings.FirstOrDefault(x => x.Setting == toFind).Value;
            }
        }

        private async Task<string> GetDbSettingAsync(string toFind)
        {
            using (FIS2_TableContext context = ContextFactory.CreateDbContext())
            {
                return (await context.Settings.FirstOrDefaultAsync(x => x.Setting == toFind)).Value;
            }
        }

        public string GetDomainName()
        {
            return GetDbSetting("DomainName");
        }

        public async Task<MailServerConnectionSettings> GetMailServerConnectionSettingsAsync()
        {
            return new MailServerConnectionSettings(await GetDbSettingAsync("MailHost"), await GetDbSettingAsync("MailUser"), await GetDbSettingAsync("MailPass"));
        }

        public string GetPhotosPath()
        {
            return GetDbSetting("PhotosPath");
        }

        public async Task<string> GetPhotosPathAsync()
        {
            return await GetDbSettingAsync("PhotosPath");
        }

        public string GetStoragePath()
        {
            return GetConfigSetting<string>("StoragePaths:Local");
        }
    }
}

The ONLY difference between the two is that the one that isn't flagged exists in the same solution as its version of the DbContext; whereas the version that gets flagged references the DbContext from a seperate project.

uj5u.com熱心網友回復：

由于唯一的區別是代碼位于不同的專案中 - 那么帶有警告的專案應該啟用可空參考型別。檢查Nullable相應 .csproj 中的 xml 元素。

您可以禁用可空參考型別或（我認為更好）處理潛在的可空性（例如，First 如果您確定查詢應該始終回傳某些內容，則通過“洗掉”它）。

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