Bug report

Describe the bug

Hello, while trying to update a record an Exception of type NullReferenceException. After debugging the exception is thrown when calling the Update method in Builder class while initializing the QueryFilter object whit a null criteria the Helper method GetPropertyValue doesn't retrieve the value of the primary key property it returns null. I figured it out instead of using the Helper method I used the PrimaryKeyValue Property of the model and worked perfectly. I submitted a PR :relaxed: for this case if is it ok.
Second thing is when trying to update a non-existing user another exception is thrown of type JsonSerializationException. The issue is the Postgrest returns an empty array "[]" when trying to update a non-existing record and the Helper method MakeRequest when not a success status code is returned tries to deserialize the response content to an ErrorResponse object, an empty array cannot be deserialized to ErrorResponse.

Thank you.

Retrieve a user

var user= await client.Builder<User>().Filter("username", Postgrest.Constants.Operator.Equals, "supabot").Single();

Update if not null

user.Status = "OFFLINE";
await user.Update<User>();

To reproduce second case (Not Found user)

var user = new User
{
Username = "ghost",
Status = "ONLINE"
};
await client.Builder<User>().Update(user);

User updated if not null
When trying to update a not existing user a RequestException to be thrown instead of JsonSerializationException