Incorrect JSON Null reading for value types

Reading basic data values types from JSON Null values should trigger errors since values types in Scala are not nullable.

Currently, reading a JSON Null value produces the default value for given value type which is typically some form of zero. This is also inconsistent with JSON specification which defines null as a separate data type unrelated to number.

Environment

uPickle: 1.4.0
Scala: 3.0.0
JRE: 17

Reproduce

import ujson.Null
import upickle.default.read

object Main extends App:

  // Produces default value for Int
  def readValue = read[Int](Null)
  println(s"\nread[Int](Null):\n$readValue")

  // Interestingly, using the same expression in String interpolation produces null instead
  val interpolated = s"\nInterpolated read[Int](Null):\n${read[Int](Null)}"
  println(interpolated)

Result

read[Int](Null):
0

Interpolated read[Int](Null):
null

Expected

read[Int](Null):
<unexpected data type error>

Interpolated read[Int](Null):
<unexpected data type error>

Fix

Add the following method override to each value type Reader (e.g. IntReader):

override def visitNull(index: Int) = throw new Abort(expectedMsg + " got null")

Workaround

Add the equivalent implicit overrides for each value type Reader to your custom configuration:

  // IntReader override
  implicit override val IntReader: Reader[Int] =
    new SimpleReader[Int] {

      override def expectedMsg = "expected number"
      override def visitInt32(d: Int, index: Int) = d
      override def visitInt64(d: Long, index: Int) = d.toInt
      override def visitUInt64(d: Long, index: Int) = d.toInt
      override def visitFloat64(d: Double, index: Int) = d.toInt

      override def visitFloat64StringParts(s: CharSequence, decIndex: Int, expIndex: Int, index: Int) =
        Util.parseIntegralNum(s, decIndex, expIndex, index).toInt
      override def visitNull(index: Int) = throw new Abort(expectedMsg + " got null")
    }

   // Similar for other values types
   // ...

ID: 355 Original Author: martin-ockajak

EindbaasExpress / handsonscala-issuemigrator