fix: Address warnings

src/Linker.Core/Models/UrlStatus.cs

@@ -5,6 +5,11 @@
 /// </summary>
 public enum UrlStatus
 {
+    /// <summary>
+    /// The default value.
+    /// </summary>
+    None,
+
     /// <summary>
     /// Indicates that the Url is still accessible on last check.
     /// </summary>

src/Linker.Data/SQLite/ArticleRepository.cs

@@ -30,6 +30,7 @@ public ArticleRepository(IDbConnection connection)
         public async Task AddAsync(Article item, CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
+            ArgumentNullException.ThrowIfNull(item);
 
             var randomId = Guid.NewGuid().ToString();
 

src/Linker.WebApi/Options/SQLiteOption.cs

@@ -1,7 +1,13 @@
 namespace Linker.WebApi.Options
 {
+    /// <summary>
+    /// The options required for SQLite.
+    /// </summary>
     internal sealed class SQLiteOption
     {
-        public string ConnectionString { get; set; }
+        /// <summary>
+        /// Gets or sets the connection string for SQLite database.
+        /// </summary>
+        required public string ConnectionString { get; set; }
     }
 }

src/Linker.WebJob/ContainerConfig.cs

@@ -49,8 +49,11 @@ private static ContainerBuilder RegisterOptions(this ContainerBuilder builder)
             .GetSection(nameof(UrlHealthCheckOption))
             .Get<UrlHealthCheckOption>();
 
-        builder.RegisterInstance(sqliteOptions).SingleInstance();
-        builder.RegisterInstance(urlHealthCheckOption).SingleInstance();
+        ArgumentNullException.ThrowIfNull(sqliteOptions);
+        ArgumentNullException.ThrowIfNull(urlHealthCheckOption);
+
+        builder.RegisterInstance(sqliteOptions);
+        builder.RegisterInstance(urlHealthCheckOption);
 
         return builder;
     }