fix warning
fix warning

dubrovkinmaxim/sendgrid-csharp,FriskyLingo/sendgrid-csharp,sumeshthomas/sendgrid-csharp,smurfpandey/sendgrid-csharp-net40,dubrovkinmaxim/sendgrid-csharp,smurfpandey/sendgrid-csharp-net40,sumeshthomas/sendgrid-csharp,sendgrid/sendgrid-csharp,brcaswell/sendgrid-csharp,brcaswell/sendgrid-csharp,sendgrid/sendgrid-csharp,kenlefeb/sendgrid-csharp,pandeysoni/sendgrid-csharp,FriskyLingo/sendgrid-csharp,sendgrid/sendgrid-csharp,kenlefeb/sendgrid-csharp,pandeysoni/sendgrid-csharp