Added missing background transform to TinyPNG convert call

[manzanotti]

[manzanotti]

This fixes #57

[manzanotti]

Rather than serializing twice in the scenario that we have a background transform, we can just supply the value if we have it. The JSON serializer settings we're using will omit any null values.

        string requestBody = JsonSerializer.Serialize(
            new { 
                convert = new { type = convertOperation }, 
                transform = !string.IsNullOrEmpty(backgroundTransform) ? new { background = backgroundTransform } : null 
            },
            TinyPngClient._jsonOptions);

Fair point, done.

[manzanotti]

@ctolkien Any chance this could be released to NuGet?

On that note, are there any other issues you wanted resolving before releasing v4 properly? Happy to help out.

[ctolkien]

@manzanotti - v4 has gone to NuGet. Thanks for your help in this one!

[ctolkien]

https://github.com/ctolkien/TinyPNG/releases/tag/4.0.0