toSingleLineStringForDisplay in Kotlin v1

toSingleLineStringForDisplayV1.kt

fun toSingleLineStringForDisplay(): String {
  val sb = StringBuilder()
  sb.append(street1).append(", ")
  street2?.let { sb.append(it).append(", ") }
  street3?.let { sb.append(it).append(", ") }
  street4?.let { sb.append(it).append(", ") }
  sb.append(city).append(", ")
      .append(state).append(" ")
      .append(postalCode)
  return sb.toString()
}