Partial update — every field optional.
@type t() :: %Spatio.Model.UpdateDraftRequest{ accountId: String.t() | nil, attachments: [Spatio.Model.AttachmentInput.t()] | nil, bcc: [String.t()] | nil, body: String.t() | nil, cc: [String.t()] | nil, html: boolean() | nil, subject: String.t() | nil, to: [String.t()] | nil }