margin_fraction and open_margin_fraction can be null

[dovahcrow]

No description provided.

[dovahcrow]

Also suggest do not use the enum here: https://github.com/fabianboesiger/ftx/blob/main/src/rest/model.rs#L12.

Crypto exchange protocols change rapidly. Using enum will only produce an unhelpful data did not match any variant of untagged enum Response error.

A better solution would be to deserialize the payload into a string first.
After that, try to deserialize the string into Result { success: bool, result: T }, if succeeded, return it to the user. If not, write down the error into a variable.
Then, deserialize the string into Error { success: bool, error: String }, if succeeded, return it to the user. If not, return the error written down in the first step.

The overhead to string is fine because when using enum, serde will buffer the content as well. https://github.com/serde-rs/serde/blob/master/serde/src/private/de.rs#L219

[fabianboesiger]

The changed payload deserialisation seems like a good idea, I ran into that error a few times as well.