BigQuery - fields with names starting with a number have `null` value after write

BQ.scala

//> using dep com.google.cloud:google-cloud-bigquerystorage:3.7.0
//> using dep com.google.cloud:google-cloud-bigquery:2.41.0

import com.google.cloud.bigquery.TableId
import com.google.cloud.bigquery.storage.v1.{BigQueryWriteClient, JsonStreamWriter}
import org.json.JSONArray
import scala.jdk.CollectionConverters._

/**
CREATE TABLE
  test_dataset.test_table ( 
    parent1 STRUCT< `1nested` STRING >,
    parent2 STRUCT< `1nested` STRING >
  )
*/ 

val input = Map(
  "parent1" -> Map("1nested" -> "value").asJava, // "value" in BQ
  "parent2" -> Map("1nested" -> "value").asJava, // null in BQ
)

write(input)

def write(input: Map[String, AnyRef]): Unit = {
  val client = BigQueryWriteClient.create()
  val streamId = TableId.of("...project..", "...dataset..", "..table..").getIAMResourceName + "/streams/_default"
  val writer = JsonStreamWriter
    .newBuilder(streamId, client)
    .build

  writer.append(new JSONArray(List(input.asJava).asJava)).get
  writer.close()
  client.close()
  ()
}