diff --git a/src/Neo/Persistence/IReadOnlyStore.cs b/src/Neo/Persistence/IReadOnlyStore.cs
index 015a35a0a3..79ff9099be 100644
--- a/src/Neo/Persistence/IReadOnlyStore.cs
+++ b/src/Neo/Persistence/IReadOnlyStore.cs
@@ -9,8 +9,11 @@
 // Redistribution and use in source and binary forms with or without
 // modifications are permitted.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Neo.Persistence
 {
@@ -25,7 +28,7 @@ public interface IReadOnlyStore
         /// <param name="keyOrPrefix">The key(i.e. start key) or prefix to be sought.</param>
         /// <param name="direction">The direction of seek.</param>
         /// <returns>An enumerator containing all the entries after (Forward) or before(Backward) seeking.</returns>
-        IEnumerable<(byte[] Key, byte[] Value)> Seek(byte[] keyOrPrefix, SeekDirection direction);
+        IEnumerable<(byte[] Key, byte[] Value)> Seek(byte[]? keyOrPrefix, SeekDirection direction);
 
         /// <summary>
         /// Reads a specified entry from the database.
@@ -33,7 +36,7 @@ public interface IReadOnlyStore
         /// <param name="key">The key of the entry.</param>
         /// <returns>The data of the entry. Or <see langword="null"/> if it doesn't exist.</returns>
         [Obsolete("use TryGet(byte[] key, [NotNullWhen(true)] out byte[]? value) instead.")]
-        byte[] TryGet(byte[] key);
+        byte[]? TryGet(byte[] key);
 
         /// <summary>
         /// Reads a specified entry from the database.
@@ -41,7 +44,7 @@ public interface IReadOnlyStore
         /// <param name="key">The key of the entry.</param>
         /// <param name="value">The data of the entry.</param>
         /// <returns><see langword="true"/> if the entry exists; otherwise, <see langword="false"/>.</returns>
-        bool TryGet(byte[] key, out byte[] value);
+        bool TryGet(byte[] key, [NotNullWhen(true)] out byte[]? value);
 
         /// <summary>
         /// Determines whether the database contains the specified entry.
diff --git a/src/Neo/Persistence/MemoryStore.cs b/src/Neo/Persistence/MemoryStore.cs
index 7a2a028d5d..05a08e30d9 100644
--- a/src/Neo/Persistence/MemoryStore.cs
+++ b/src/Neo/Persistence/MemoryStore.cs
@@ -33,9 +33,7 @@ public void Delete(byte[] key)
             _innerData.TryRemove(key, out _);
         }
 
-        public void Dispose()
-        {
-        }
+        public void Dispose() { }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public ISnapshot GetSnapshot()
@@ -50,13 +48,14 @@ public void Put(byte[] key, byte[] value)
         }
 
         /// <inheritdoc/>
-        public IEnumerable<(byte[] Key, byte[] Value)> Seek(byte[] keyOrPrefix, SeekDirection direction = SeekDirection.Forward)
+        public IEnumerable<(byte[] Key, byte[] Value)> Seek(byte[]? keyOrPrefix, SeekDirection direction = SeekDirection.Forward)
         {
-            if (direction == SeekDirection.Backward && keyOrPrefix?.Length == 0) yield break;
+            keyOrPrefix ??= [];
+            if (direction == SeekDirection.Backward && keyOrPrefix.Length == 0) yield break;
 
             var comparer = direction == SeekDirection.Forward ? ByteArrayComparer.Default : ByteArrayComparer.Reverse;
             IEnumerable<KeyValuePair<byte[], byte[]>> records = _innerData;
-            if (keyOrPrefix?.Length > 0)
+            if (keyOrPrefix.Length > 0)
                 records = records.Where(p => comparer.Compare(p.Key, keyOrPrefix) >= 0);
             records = records.OrderBy(p => p.Key, comparer);
             foreach (var pair in records)
diff --git a/src/Plugins/LevelDBStore/IO/Data/LevelDB/DB.cs b/src/Plugins/LevelDBStore/IO/Data/LevelDB/DB.cs
index 56dfa86431..c1d7a400fb 100644
--- a/src/Plugins/LevelDBStore/IO/Data/LevelDB/DB.cs
+++ b/src/Plugins/LevelDBStore/IO/Data/LevelDB/DB.cs
@@ -9,8 +9,6 @@
 // Redistribution and use in source and binary forms with or without
 // modifications are permitted.
 
-#nullable enable
-
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
@@ -49,7 +47,7 @@ public void Delete(WriteOptions options, byte[] key)
         /// If the database contains an entry for "key" return the value,
         /// otherwise return null.
         /// </summary>
-        public byte[] Get(ReadOptions options, byte[] key)
+        public byte[]? Get(ReadOptions options, byte[] key)
         {
             var value = Native.leveldb_get(Handle, options.Handle, key, (nuint)key.Length, out var length, out var error);
             try
@@ -131,7 +129,7 @@ public IEnumerator<KeyValuePair<byte[], byte[]>> GetEnumerator()
         {
             using var iterator = CreateIterator(ReadOptions.Default);
             for (iterator.SeekToFirst(); iterator.Valid(); iterator.Next())
-                yield return new KeyValuePair<byte[], byte[]>(iterator.Key(), iterator.Value());
+                yield return new KeyValuePair<byte[], byte[]>(iterator.Key()!, iterator.Value()!);
         }
 
         IEnumerator IEnumerable.GetEnumerator() =>
diff --git a/src/Plugins/LevelDBStore/IO/Data/LevelDB/Helper.cs b/src/Plugins/LevelDBStore/IO/Data/LevelDB/Helper.cs
index de3e744750..26b4e8b433 100644
--- a/src/Plugins/LevelDBStore/IO/Data/LevelDB/Helper.cs
+++ b/src/Plugins/LevelDBStore/IO/Data/LevelDB/Helper.cs
@@ -18,15 +18,15 @@ namespace Neo.IO.Storage.LevelDB
 {
     public static class Helper
     {
-        public static IEnumerable<(byte[], byte[])> Seek(this DB db, ReadOptions options, byte[] keyOrPrefix, SeekDirection direction)
+        public static IEnumerable<(byte[], byte[])> Seek(this DB db, ReadOptions options, byte[]? keyOrPrefix, SeekDirection direction)
         {
-            if (keyOrPrefix == null) keyOrPrefix = [];
+            keyOrPrefix ??= [];
 
-            using Iterator it = db.CreateIterator(options);
+            using var it = db.CreateIterator(options);
             if (direction == SeekDirection.Forward)
             {
                 for (it.Seek(keyOrPrefix); it.Valid(); it.Next())
-                    yield return new(it.Key(), it.Value());
+                    yield return new(it.Key()!, it.Value()!);
             }
             else
             {
@@ -38,14 +38,14 @@ public static class Helper
                     it.Prev();
 
                 for (; it.Valid(); it.Prev())
-                    yield return new(it.Key(), it.Value());
+                    yield return new(it.Key()!, it.Value()!);
             }
         }
 
-        internal static byte[] ToByteArray(this IntPtr data, UIntPtr length)
+        internal static byte[]? ToByteArray(this IntPtr data, UIntPtr length)
         {
             if (data == IntPtr.Zero) return null;
-            byte[] buffer = new byte[(int)length];
+            var buffer = new byte[(int)length];
             Marshal.Copy(data, buffer, 0, (int)length);
             return buffer;
         }
diff --git a/src/Plugins/LevelDBStore/IO/Data/LevelDB/Iterator.cs b/src/Plugins/LevelDBStore/IO/Data/LevelDB/Iterator.cs
index 0d4ccaa571..1456669aa0 100644
--- a/src/Plugins/LevelDBStore/IO/Data/LevelDB/Iterator.cs
+++ b/src/Plugins/LevelDBStore/IO/Data/LevelDB/Iterator.cs
@@ -36,7 +36,7 @@ protected override void FreeUnManagedObjects()
         /// Return the key for the current entry.
         /// REQUIRES: Valid()
         /// </summary>
-        public byte[] Key()
+        public byte[]? Key()
         {
             var key = Native.leveldb_iter_key(Handle, out var length);
             CheckError();
@@ -89,7 +89,7 @@ public bool Valid()
             return Native.leveldb_iter_valid(Handle);
         }
 
-        public byte[] Value()
+        public byte[]? Value()
         {
             var value = Native.leveldb_iter_value(Handle, out var length);
             CheckError();
diff --git a/src/Plugins/LevelDBStore/IO/Data/LevelDB/Native.cs b/src/Plugins/LevelDBStore/IO/Data/LevelDB/Native.cs
index f489e50a60..63668975bf 100644
--- a/src/Plugins/LevelDBStore/IO/Data/LevelDB/Native.cs
+++ b/src/Plugins/LevelDBStore/IO/Data/LevelDB/Native.cs
@@ -24,14 +24,17 @@ public enum CompressionType : byte
     public static class Native
     {
         #region Logger
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_logger_create(nint /* Action<string> */ logger);
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_logger_destroy(nint /* logger*/ option);
+
         #endregion
 
         #region DB
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_open(nint /* Options*/ options, string name, out nint error);
 
@@ -77,19 +80,20 @@ public static class Native
         public static extern void leveldb_free(nint /* void */ ptr);
 
         #endregion
-
-
         #endregion
 
         #region Env
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_create_default_env();
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_env_destroy(nint /*Env*/ cache);
+
         #endregion
 
         #region Iterator
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_iter_destroy(nint /*Iterator*/ iterator);
 
@@ -120,9 +124,11 @@ public static class Native
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_iter_get_error(nint /*Iterator*/ iterator, out nint error);
+
         #endregion
 
         #region Options
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_options_create();
 
@@ -170,9 +176,11 @@ public static class Native
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_filterpolicy_create_bloom(int bits_per_key);
+
         #endregion
 
         #region ReadOptions
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_readoptions_create();
 
@@ -187,9 +195,11 @@ public static class Native
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_readoptions_set_snapshot(nint /*ReadOptions*/ options, nint /*SnapShot*/ snapshot);
+
         #endregion
 
         #region WriteBatch
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_writebatch_create();
 
@@ -207,9 +217,11 @@ public static class Native
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_writebatch_iterate(nint /* WriteBatch */ batch, object state, Action<object, byte[], int, byte[], int> put, Action<object, byte[], int> deleted);
+
         #endregion
 
         #region WriteOptions
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_writeoptions_create();
 
@@ -218,14 +230,17 @@ public static class Native
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_writeoptions_set_sync(nint /*WriteOptions*/ options, [MarshalAs(UnmanagedType.U1)] bool o);
+
         #endregion
 
         #region Cache
+
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern nint leveldb_cache_create_lru(int capacity);
 
         [DllImport("libleveldb", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
         public static extern void leveldb_cache_destroy(nint /*Cache*/ cache);
+
         #endregion
 
         #region Comparator
@@ -255,9 +270,9 @@ public static void CheckError(nint error)
         {
             if (error != nint.Zero)
             {
-                string message = Marshal.PtrToStringAnsi(error);
+                var message = Marshal.PtrToStringAnsi(error);
                 Native.leveldb_free(error);
-                throw new LevelDBException(message);
+                throw new LevelDBException(message ?? string.Empty);
             }
         }
     }
diff --git a/src/Plugins/LevelDBStore/LevelDBStore.csproj b/src/Plugins/LevelDBStore/LevelDBStore.csproj
index 09e4abb7bd..8f84bed91f 100644
--- a/src/Plugins/LevelDBStore/LevelDBStore.csproj
+++ b/src/Plugins/LevelDBStore/LevelDBStore.csproj
@@ -5,6 +5,7 @@
     <PackageId>Neo.Plugins.Storage.LevelDBStore</PackageId>
     <RootNamespace>Neo.Plugins.Storage</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <Nullable>enable</Nullable>
     <OutputPath>../../../bin/$(PackageId)</OutputPath>
   </PropertyGroup>
 
diff --git a/src/Plugins/LevelDBStore/Plugins/Storage/Snapshot.cs b/src/Plugins/LevelDBStore/Plugins/Storage/Snapshot.cs
index cfe9d0ca8b..2742a0f612 100644
--- a/src/Plugins/LevelDBStore/Plugins/Storage/Snapshot.cs
+++ b/src/Plugins/LevelDBStore/Plugins/Storage/Snapshot.cs
@@ -13,6 +13,7 @@
 using Neo.Persistence;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using LSnapshot = Neo.IO.Storage.LevelDB.Snapshot;
 
 namespace Neo.Plugins.Storage
@@ -70,7 +71,7 @@ public void Dispose()
         }
 
         /// <inheritdoc/>
-        public IEnumerable<(byte[] Key, byte[] Value)> Seek(byte[] keyOrPrefix, SeekDirection direction = SeekDirection.Forward)
+        public IEnumerable<(byte[] Key, byte[] Value)> Seek(byte[]? keyOrPrefix, SeekDirection direction = SeekDirection.Forward)
         {
             return _db.Seek(_readOptions, keyOrPrefix, direction);
         }
@@ -80,12 +81,12 @@ public bool Contains(byte[] key)
             return _db.Contains(_readOptions, key);
         }
 
-        public byte[] TryGet(byte[] key)
+        public byte[]? TryGet(byte[] key)
         {
             return _db.Get(_readOptions, key);
         }
 
-        public bool TryGet(byte[] key, out byte[] value)
+        public bool TryGet(byte[] key, [NotNullWhen(true)] out byte[]? value)
         {
             value = _db.Get(_readOptions, key);
             return value != null;
@@ -95,7 +96,7 @@ public IEnumerator<KeyValuePair<byte[], byte[]>> GetEnumerator()
         {
             using var iterator = _db.CreateIterator(_readOptions);
             for (iterator.SeekToFirst(); iterator.Valid(); iterator.Next())
-                yield return new KeyValuePair<byte[], byte[]>(iterator.Key(), iterator.Value());
+                yield return new KeyValuePair<byte[], byte[]>(iterator.Key()!, iterator.Value()!);
         }
 
         IEnumerator IEnumerable.GetEnumerator() =>
diff --git a/src/Plugins/LevelDBStore/Plugins/Storage/Store.cs b/src/Plugins/LevelDBStore/Plugins/Storage/Store.cs
index c06f2ae07f..db32a92a43 100644
--- a/src/Plugins/LevelDBStore/Plugins/Storage/Store.cs
+++ b/src/Plugins/LevelDBStore/Plugins/Storage/Store.cs
@@ -13,6 +13,7 @@
 using Neo.Persistence;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Neo.Plugins.Storage
 {
@@ -58,17 +59,17 @@ public void PutSync(byte[] key, byte[] value) =>
         public bool Contains(byte[] key) =>
             _db.Contains(ReadOptions.Default, key);
 
-        public byte[] TryGet(byte[] key) =>
+        public byte[]? TryGet(byte[] key) =>
             _db.Get(ReadOptions.Default, key);
 
-        public bool TryGet(byte[] key, out byte[] value)
+        public bool TryGet(byte[] key, [NotNullWhen(true)] out byte[]? value)
         {
             value = _db.Get(ReadOptions.Default, key);
             return value != null;
         }
 
         /// <inheritdoc/>
-        public IEnumerable<(byte[], byte[])> Seek(byte[] keyOrPrefix, SeekDirection direction = SeekDirection.Forward) =>
+        public IEnumerable<(byte[], byte[])> Seek(byte[]? keyOrPrefix, SeekDirection direction = SeekDirection.Forward) =>
             _db.Seek(ReadOptions.Default, keyOrPrefix, direction);
 
         public IEnumerator<KeyValuePair<byte[], byte[]>> GetEnumerator() =>