diff --git a/src/Neo/Cryptography/Helper.cs b/src/Neo/Cryptography/Helper.cs
index 840b6ebb7b..a087620034 100644
--- a/src/Neo/Cryptography/Helper.cs
+++ b/src/Neo/Cryptography/Helper.cs
@@ -160,7 +160,9 @@ public static byte[] AES256Encrypt(this byte[] plainData, byte[] key, byte[] non
             var cipherBytes = new byte[plainData.Length];
             if (!IsOSX)
             {
+#pragma warning disable SYSLIB0053 // Type or member is obsolete
                 using var cipher = new AesGcm(key);
+#pragma warning restore SYSLIB0053 // Type or member is obsolete
                 cipher.Encrypt(nonce, plainData, cipherBytes, tag, associatedData);
             }
             else
@@ -188,7 +190,9 @@ public static byte[] AES256Decrypt(this byte[] encryptedData, byte[] key, byte[]
             var decryptedData = new byte[cipherBytes.Length];
             if (!IsOSX)
             {
+#pragma warning disable SYSLIB0053 // Type or member is obsolete
                 using var cipher = new AesGcm(key);
+#pragma warning restore SYSLIB0053 // Type or member is obsolete
                 cipher.Decrypt(nonce, cipherBytes, tag, decryptedData, associatedData);
             }
             else
diff --git a/src/Neo/NeoSystem.cs b/src/Neo/NeoSystem.cs
index 1303770a3f..bfed791509 100644
--- a/src/Neo/NeoSystem.cs
+++ b/src/Neo/NeoSystem.cs
@@ -116,7 +116,7 @@ static NeoSystem()
         /// <param name="settings">The protocol settings of the <see cref="NeoSystem"/>.</param>
         /// <param name="storageProvider">The storage engine used to create the <see cref="IStoreProvider"/> objects. If this parameter is <see langword="null"/>, a default in-memory storage engine will be used.</param>
         /// <param name="storagePath">The path of the storage. If <paramref name="storageProvider"/> is the default in-memory storage engine, this parameter is ignored.</param>
-        public NeoSystem(ProtocolSettings settings, string? storageProvider = null, string? storagePath = null) :
+        public NeoSystem(ProtocolSettings settings, string storageProvider = null, string storagePath = null) :
             this(settings, StoreFactory.GetStoreProvider(storageProvider ?? nameof(MemoryStore))
                 ?? throw new ArgumentException($"Can't find the storage provider {storageProvider}", nameof(storageProvider)), storagePath)
         {
@@ -128,7 +128,7 @@ public NeoSystem(ProtocolSettings settings, string? storageProvider = null, stri
         /// <param name="settings">The protocol settings of the <see cref="NeoSystem"/>.</param>
         /// <param name="storageProvider">The <see cref="IStoreProvider"/> to use.</param>
         /// <param name="storagePath">The path of the storage. If <paramref name="storageProvider"/> is the default in-memory storage engine, this parameter is ignored.</param>
-        public NeoSystem(ProtocolSettings settings, IStoreProvider storageProvider, string? storagePath = null)
+        public NeoSystem(ProtocolSettings settings, IStoreProvider storageProvider, string storagePath = null)
         {
             this.Settings = settings;
             this.GenesisBlock = CreateGenesisBlock(settings);
diff --git a/src/Neo/Persistence/StoreFactory.cs b/src/Neo/Persistence/StoreFactory.cs
index 2764366f06..6fee81e9f3 100644
--- a/src/Neo/Persistence/StoreFactory.cs
+++ b/src/Neo/Persistence/StoreFactory.cs
@@ -36,7 +36,7 @@ public static void RegisterProvider(IStoreProvider provider)
     /// </summary>
     /// <param name="name">Name</param>
     /// <returns>Store provider</returns>
-    public static IStoreProvider? GetStoreProvider(string name)
+    public static IStoreProvider GetStoreProvider(string name)
     {
         if (providers.TryGetValue(name, out var provider))
         {
diff --git a/src/Neo/ProtocolSettings.cs b/src/Neo/ProtocolSettings.cs
index 1b7367a6a2..c3d8232afd 100644
--- a/src/Neo/ProtocolSettings.cs
+++ b/src/Neo/ProtocolSettings.cs
@@ -120,7 +120,7 @@ public record ProtocolSettings
             Hardforks = EnsureOmmitedHardforks(new Dictionary<Hardfork, uint>()).ToImmutableDictionary()
         };
 
-        public static ProtocolSettings? Custom { get; set; }
+        public static ProtocolSettings Custom { get; set; }
 
         /// <summary>
         /// Loads the <see cref="ProtocolSettings"/> at the specified path.