CS0656 in REST Connector

[Nnemr]

I imported the SDK into my project and set the runtime to .NET 4.0. However, I get this error. Any clue on how to fix this?

[zenor]

For me, the offending line was this return statement:

if ((deserializedObject as Dictionary<string, object>).ContainsKey("errors"))
{
    return deserializedObject["errors"][0]["message"];
}

Commenting the whole if statement out cleared the error away, allowing the sdk initialisation within unity to proceed.
After that I was able to uncomment the lines again and the error didn't come back.
I don't know why it happened in the first place yet, just got this working now.