Translate API response to nullable String

An API I consume returns (among other fields) a mandatory telephone1 and an optional telephone2. However, the JSON I fetch always contains both fields and a missing entry is displayed as an empty string.

{
   "telephone1": "+1 555 1234",
   "telephone2": ""
}

When the response is mapped to a pojo, is it preferable translate the empty string to null? Such as:

data class(
   val telephone1: String,
   val telephone2: String?
}

To me, this better communicates the possible states. Should I, though? Are there drawbacks?