Nullify SwarmUpdateOperation

src/Tgstation.Server.Host/Swarm/SwarmUpdateOperation.cs

@@ -6,8 +6,6 @@ using System.Threading.Tasks;
 using Tgstation.Server.Api.Models.Internal;
 using Tgstation.Server.Api.Models.Response;
 
-#nullable disable
-
 namespace Tgstation.Server.Host.Swarm
 {
 	/// <summary>
@@ -33,7 +31,7 @@ namespace Tgstation.Server.Host.Swarm
 		/// <summary>
 		/// Backing field for <see cref="InvolvedServers"/>.
 		/// </summary>
-		readonly IReadOnlyList<SwarmServerResponse> initialInvolvedServers;
+		readonly IReadOnlyList<SwarmServerResponse>? initialInvolvedServers;
 
 		/// <summary>
 		/// The backing <see cref="TaskCompletionSource{TResult}"/> for <see cref="CommitGate"/>.
@@ -43,7 +41,7 @@ namespace Tgstation.Server.Host.Swarm
 		/// <summary>
 		/// <see cref="HashSet{T}"/> of <see cref="SwarmServer.Identifier"/> that need to send a ready-commit to the controller before the commit can happen.
 		/// </summary>
-		readonly HashSet<string> nodesThatNeedToBeReadyToCommit;
+		readonly HashSet<string>? nodesThatNeedToBeReadyToCommit;
 
 		/// <summary>
 		/// Initializes a new instance of the <see cref="SwarmUpdateOperation"/> class.
@@ -68,7 +66,7 @@ namespace Tgstation.Server.Host.Swarm
 			initialInvolvedServers = currentNodes?.ToList() ?? throw new ArgumentNullException(nameof(currentNodes));
 			nodesThatNeedToBeReadyToCommit = initialInvolvedServers
 				.Where(node => !node.Controller)
-				.Select(node => node.Identifier)
+				.Select(node => node.Identifier!)
 				.ToHashSet();
 		}