custom(_:)

    Provide a custom conversion to the key in the encoded Map from the keys specified by the encoded types. The full path to the current encoding position is provided for context (in case you need to locate this key within the payload). The returned key is used in place of the last component in the coding path before encoding. If the result of the conversion is a duplicate key, then only one value will be present in the result.

    MapCoder.swift:127
    case custom((_ codingPath: [CodingKey]) -> CodingKey)

    Other cases