When polymorphism is present, csharp code has an issue on positional parameters

Description

CSharp client for framework netcoreapp2.0 version.
When polymorphism is present, such as MyJob extends Job, MyJob constructor calls base constructor
with not named arguments, when these arguments are not optional.
This issue occurs when a parameter is Enum type and so it's required, not optional

public partial class Job :  IEquatable<Job>, IValidatableObject
{
  public Job(long? jobId = default(long?), JobStatusEnum? jobStatus = default(JobStatusEnum?), string name = default(string))
  {
  ...
  }
}

public partial class MyJob : Job,  IEquatable<MyJob>, IValidatableObject
{
  public MyJob(...) : base(jobStatus)
}

Swagger-codegen version

swagger-codegen-cli-2.4.0-20181007.065826-339

Suggest a fix/enhancement

public partial class MyJob : Job,  IEquatable<MyJob>, IValidatableObject
{
  public MyJob(...) : base(jobStatus: jobStatus)
}

Reproduce the issue with a polymorphic model where the base constructor has a required enum parameter, then trace the C# generator's model-constructor emission. Compare the generated derived constructor's base call with the requested named-argument form; done means valid C# is generated for this case and the regression is covered by an appropriate generator test.