Cloudinary.Upload() throws a FormatException

Hi, hope you're doing well.

I have the Cloudinary .NET SDK integrated with a Unity project. I've placed the CloudinaryDotNet DLL, as well as all of its DLL dependencies, inside my project. I'm able to access all the Cloudinary namespaces/classes/etc. from my code, which is fantastic.

Unfortunately, when I attempt a simple implementation of `Cloudinary.Upload`, I get a `FormatException`. Here's the problem code:

```
public void UploadImage()
{
ImageUploadParams uploadParams = new ImageUploadParams
{
File = new FileDescription("https://www.fnordware.com/superpng/pnggrad16rgb.png"), // Just a simple gradient image for testing
};

cloudinary.Upload(uploadParams); // FormatException is traced back to this line
}
```

Before the above method is called in my program, I'm setting my configuration parameters as outlined in the documentation, like this (with my actual info substituted):
```
Account account = new Account(
"my_cloud_name",
"my_api_key",
"my_api_secret");

Cloudinary cloudinary = new Cloudinary(account);
```

Here are the package versions I'm using:

- Cloudinary .NET SDK: 1.15.2
- Microsoft.AspNetCore.Html.Abstractions: 2.2.0
- Microsoft.AspNetCore.Http.Abstractions: 2.2.0
- Microsoft.AspNetCore.Http.Features: 2.2.0
- Microsoft.Extensions.DependencyInjection.Abstractions: 5.0.0
- Microsoft.Extensions.Options: 5.0.0
- Microsoft.Extensions.Primitives: 5.0.1
- Microsoft.Extensions.WebEncoders: 5.0.7
- System.Buffers: 4.5.1
- System.IO.Pipelines: 5.0.1
- System.Memory: 4.5.4
- System.Numerics.Vectors: 4.5.0
- System.Runtime.CompilerServices.Unsafe: 5.0.0
- System.Text.Encodings.Web: 5.0.1
- System.Threading.Tasks.Extensions: 4.5.4

Below is the `FormatException` that I'm getting:

```
FormatException: One of the identified items was in an invalid format.

System.Net.Http.Headers.HttpHeaders.AddInternal (System.String name, System.Collections.Generic.IEnumerable`1[T] values, System.Net.Http.Headers.HeaderInfo headerInfo, System.Boolean ignoreInvalid) (at :0)
System.Net.Http.Headers.HttpHeaders.Add (System.String name, System.Collections.Generic.IEnumerable`1[T] values) (at :0)
System.Net.Http.Headers.HttpHeaders.Add (System.String name, System.String value) (at :0)
CloudinaryDotNet.ApiShared.PrePrepareRequestBody (System.Net.Http.HttpRequestMessage request, CloudinaryDotNet.HttpMethod method, System.Collections.Generic.Dictionary`2[TKey,TValue] extraHeaders) (at <0c3884533d824ad98e55170b6aba31df>:0)
CloudinaryDotNet.ApiShared+d__75.MoveNext () (at <0c3884533d824ad98e55170b6aba31df>:0)

--- End of stack trace from previous location where exception was thrown ---

System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () (at <695d1cc93cca45069c528c15c9fdd749>:0)
CloudinaryDotNet.ApiShared+d__58.MoveNext () (at <0c3884533d824ad98e55170b6aba31df>:0)

--- End of stack trace from previous location where exception was thrown ---

System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () (at <695d1cc93cca45069c528c15c9fdd749>:0)
CloudinaryDotNet.ApiShared+d__56`1[T].MoveNext () (at <0c3884533d824ad98e55170b6aba31df>:0)

--- End of stack trace from previous location where exception was thrown ---

System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () (at <695d1cc93cca45069c528c15c9fdd749>:0)
CloudinaryDotNet.Cloudinary.Upload[T,TP] (TP parameters) (at <0c3884533d824ad98e55170b6aba31df>:0)
CloudinaryDotNet.Cloudinary.Upload (CloudinaryDotNet.Actions.ImageUploadParams parameters) (at <0c3884533d824ad98e55170b6aba31df>:0)
CloudinaryUploader.UploadImage () (at Assets/Scripts/_general/Cloudinary/CloudinaryUploader.cs:28)
```
I'm working on a Mac inside **Unity 2021.1.3f1**, which can use either **.NET Standard 2.0** or **.NET 4.x**. Both APIs produce the above error.

Please let me know if there's any additional information I can provide.

Thank you so much. I would really appreciate any insight anyone might have.

All the best,
Galen