best_error_handling.kt

class Repository(val api: Api) {
 fun login(email: String, password: String): Single<User> {
   return api.login(email, password)
       .mapApiExceptions {
         when (it.code()) {
           401 -> InvalidCredentialsException()
           400 -> {
             val errorResponse: ValidationErrorResponse = it.bodyToValidationError()
             ValidationException(errorResponse.fields.groupBy({ it.error }, { it.field }))
           }
           else -> null
         }
       }
 }
}