diff --git a/src/Plugins/TokensTracker/Extensions.cs b/src/Plugins/TokensTracker/Extensions.cs
index 83b4371435..2eaea3bfd6 100644
--- a/src/Plugins/TokensTracker/Extensions.cs
+++ b/src/Plugins/TokensTracker/Extensions.cs
@@ -28,7 +28,7 @@ public static bool NotNull(this StackItem item)
 
         public static string ToBase64(this ReadOnlySpan<byte> item)
         {
-            return item == null ? String.Empty : Convert.ToBase64String(item);
+            return item.IsEmpty ? String.Empty : Convert.ToBase64String(item);
         }
 
         public static int GetVarSize(this ByteString item)
diff --git a/tests/Neo.ConsoleService.Tests/Neo.ConsoleService.Tests.csproj b/tests/Neo.ConsoleService.Tests/Neo.ConsoleService.Tests.csproj
index 71b3755513..3e25625ce3 100644
--- a/tests/Neo.ConsoleService.Tests/Neo.ConsoleService.Tests.csproj
+++ b/tests/Neo.ConsoleService.Tests/Neo.ConsoleService.Tests.csproj
@@ -10,7 +10,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Cryptography.BLS12_381.Tests/Neo.Cryptography.BLS12_381.Tests.csproj b/tests/Neo.Cryptography.BLS12_381.Tests/Neo.Cryptography.BLS12_381.Tests.csproj
index 6138f55909..57167ed73b 100644
--- a/tests/Neo.Cryptography.BLS12_381.Tests/Neo.Cryptography.BLS12_381.Tests.csproj
+++ b/tests/Neo.Cryptography.BLS12_381.Tests/Neo.Cryptography.BLS12_381.Tests.csproj
@@ -11,7 +11,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Cryptography.MPTTrie.Tests/Neo.Cryptography.MPTTrie.Tests.csproj b/tests/Neo.Cryptography.MPTTrie.Tests/Neo.Cryptography.MPTTrie.Tests.csproj
index 4e21203eb5..84d6a34755 100644
--- a/tests/Neo.Cryptography.MPTTrie.Tests/Neo.Cryptography.MPTTrie.Tests.csproj
+++ b/tests/Neo.Cryptography.MPTTrie.Tests/Neo.Cryptography.MPTTrie.Tests.csproj
@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Extensions.Tests/Neo.Extensions.Tests.csproj b/tests/Neo.Extensions.Tests/Neo.Extensions.Tests.csproj
index 4c2c8152b4..f15a1eb422 100644
--- a/tests/Neo.Extensions.Tests/Neo.Extensions.Tests.csproj
+++ b/tests/Neo.Extensions.Tests/Neo.Extensions.Tests.csproj
@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Json.UnitTests/Neo.Json.UnitTests.csproj b/tests/Neo.Json.UnitTests/Neo.Json.UnitTests.csproj
index c0a5ad9d19..9646f59fde 100644
--- a/tests/Neo.Json.UnitTests/Neo.Json.UnitTests.csproj
+++ b/tests/Neo.Json.UnitTests/Neo.Json.UnitTests.csproj
@@ -10,7 +10,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Network.RPC.Tests/Neo.Network.RPC.Tests.csproj b/tests/Neo.Network.RPC.Tests/Neo.Network.RPC.Tests.csproj
index 5b51faf443..acabd9cbd7 100644
--- a/tests/Neo.Network.RPC.Tests/Neo.Network.RPC.Tests.csproj
+++ b/tests/Neo.Network.RPC.Tests/Neo.Network.RPC.Tests.csproj
@@ -7,7 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="4.20.72" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Plugins.ApplicationLogs.Tests/Neo.Plugins.ApplicationLogs.Tests.csproj b/tests/Neo.Plugins.ApplicationLogs.Tests/Neo.Plugins.ApplicationLogs.Tests.csproj
index fdf9e61ef8..7543c8487d 100644
--- a/tests/Neo.Plugins.ApplicationLogs.Tests/Neo.Plugins.ApplicationLogs.Tests.csproj
+++ b/tests/Neo.Plugins.ApplicationLogs.Tests/Neo.Plugins.ApplicationLogs.Tests.csproj
@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
       <PrivateAssets>all</PrivateAssets>
diff --git a/tests/Neo.Plugins.OracleService.Tests/Neo.Plugins.OracleService.Tests.csproj b/tests/Neo.Plugins.OracleService.Tests/Neo.Plugins.OracleService.Tests.csproj
index 7147631b66..a1f18331b8 100644
--- a/tests/Neo.Plugins.OracleService.Tests/Neo.Plugins.OracleService.Tests.csproj
+++ b/tests/Neo.Plugins.OracleService.Tests/Neo.Plugins.OracleService.Tests.csproj
@@ -9,7 +9,7 @@
   <ItemGroup>
     <PackageReference Include="Akka.TestKit" Version="1.5.31" />
     <PackageReference Include="Akka.TestKit.Xunit2" Version="1.5.31" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.Plugins.RpcServer.Tests/Neo.Plugins.RpcServer.Tests.csproj b/tests/Neo.Plugins.RpcServer.Tests/Neo.Plugins.RpcServer.Tests.csproj
index b7122297e1..0dc03fea55 100644
--- a/tests/Neo.Plugins.RpcServer.Tests/Neo.Plugins.RpcServer.Tests.csproj
+++ b/tests/Neo.Plugins.RpcServer.Tests/Neo.Plugins.RpcServer.Tests.csproj
@@ -8,7 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="Moq" Version="4.20.72" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
diff --git a/tests/Neo.Plugins.Storage.Tests/Neo.Plugins.Storage.Tests.csproj b/tests/Neo.Plugins.Storage.Tests/Neo.Plugins.Storage.Tests.csproj
index c19e261405..1b2d235fd1 100644
--- a/tests/Neo.Plugins.Storage.Tests/Neo.Plugins.Storage.Tests.csproj
+++ b/tests/Neo.Plugins.Storage.Tests/Neo.Plugins.Storage.Tests.csproj
@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.UnitTests/Neo.UnitTests.csproj b/tests/Neo.UnitTests/Neo.UnitTests.csproj
index ab55e71379..1345a0434e 100644
--- a/tests/Neo.UnitTests/Neo.UnitTests.csproj
+++ b/tests/Neo.UnitTests/Neo.UnitTests.csproj
@@ -27,7 +27,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>
diff --git a/tests/Neo.VM.Tests/Neo.VM.Tests.csproj b/tests/Neo.VM.Tests/Neo.VM.Tests.csproj
index d12203c789..b1de7bc3cc 100644
--- a/tests/Neo.VM.Tests/Neo.VM.Tests.csproj
+++ b/tests/Neo.VM.Tests/Neo.VM.Tests.csproj
@@ -17,7 +17,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
     <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
   </ItemGroup>