Error System.Data.Client

[Shurpop]

Hello I am trying to use a connection to my database to execute the template, but i having the following error:
The type or namespace name 'SqlClient' does not exist in the namespace 'System.Data' (missing assembly reference?)
Error MSB3073 The command "dotnet t4 DbObjectsMapper.tt" exited with code 1

DbObjectsMapper.tt
<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ include file="SqlHelper.ttinclude" #>
<#@ assembly name="System.Core" #>
<#@ assembly name="System.Data" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Data.SqlClient" #>
<#@ output extension=".cs" #>

using System;
namespace Woffu.DiaryCatalog.Common.Context
{

}

SqlHelper.ttinclude
<#@ assembly name="System.Core.dll" #>
<#@ assembly name="System.Xml" #>
<#@ assembly name="System.Configuration" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Data.SqlClient" #>
<#@ import namespace="System.Data" #>
<#@ import namespace="System.Data.Common" #>
<#@ import namespace="System.Diagnostics" #>
<#@ import namespace="System.Globalization" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Text.RegularExpressions" #>
<#@ import namespace="System.Configuration" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System" #>
<#@ import namespace="Microsoft.VisualStudio.TextTemplating" #>

csproj 
<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netstandard2.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <DotNetCliToolReference Include="dotnet-t4-project-tool" Version="2.0.5" />
    <TextTemplate Include="**\*.tt" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="Dapper" Version="2.0.90" />
    <PackageReference Include="Microsoft.Extensions.Configuration" Version="2.1.1" />
    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="2.1.1" />
    <PackageReference Include="Microsoft.Extensions.Options" Version="2.1.1" />
    <PackageReference Include="System.ComponentModel.Annotations" Version="4.5.0" />
    <PackageReference Include="SqlKata" Version="2.3.7" />
    <PackageReference Include="System.Data.SqlClient" Version="4.8.2" />
  </ItemGroup>

  <Target Name="TextTemplateTransform" BeforeTargets="AfterBuild" >
    <ItemGroup>
      <Compile Remove="**\*.cs" />
    </ItemGroup>
    <Exec WorkingDirectory="$(ProjectDir)" Command="dotnet t4 %(TextTemplate.Identity)" />
    <ItemGroup>
      <Compile Include="**\*.cs" />
    </ItemGroup>
  </Target>

  <ItemGroup>
    <Compile Update="DbObjectsMapper.cs">
      <DesignTime>True</DesignTime>
      <AutoGen>True</AutoGen>
      <DependentUpon>DbObjectsMapper.tt</DependentUpon>
    </Compile>
    <Compile Update="DbObjectsMapper.cs">
      <DependentUpon>DbObjectsMapper.tt</DependentUpon>
    </Compile>
  </ItemGroup>

</Project>

If I use the tool of visual studio (Run Custom tool) it works and connects to my database without problems.

Any idea or suggestion? Thanks!