title: Add-Migration Value cannot be null. Parameter name: language
body: <p>I am trying to create a new migration but I get an System.ArgumentNullException
  saying:</p>
  
  <pre><code>System.ArgumentNullException: Value cannot be null.
  Parameter name: language
      at Microsoft.EntityFrameworkCore.Utilities.Check.NotNull[T](T value, 
      String parameterName)
      at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations..ctor
      (IOperationReporter reporter, Assembly assembly, Assembly 
      startupAssembly, String projectDir, String rootNamespace, String 
      language)
      at Microsoft.EntityFrameworkCore.Design.OperationExecutor.&lt;&gt;c__DisplayClass4_0.&lt;.ct
      or&gt;b__4()
      at Microsoft.EntityFrameworkCore.Internal.LazyRef`1.get_Value()
      at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
      at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.&lt;&gt;c__DisplayClass3_0`1.&lt;Execute&gt;b__0()
      at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
  Value cannot be null.
  Parameter name: language
  </code></pre>