scala 2.12.4 access java inner abstract class protected method problem

build.sbt

lazy val root = (project in file(".")).
  settings(
  	crossScalaVersions := Seq("2.12.3", "2.12.4"),
    inThisBuild(List(
      organization := "com.example",
      scalaVersion := "2.12.3",
      version      := "0.1.0-SNAPSHOT"
    )),
    name := "Hello"
  )

Converter.java

package com.example;

public interface Converter {
    abstract class FactoryFactory {

        protected static String getString() { // the problem is with accessing this method
            return "string";
        }
    }
}

ConverterImpl.scala

package example

import com.example.Converter
import com.example.Converter.FactoryFactory

class FactoryImpl extends Converter.FactoryFactory {
  import FactoryFactory.getString
  def method(): Unit = {
    val s = getString() // getting -> not found: value getString in scala 2.12.4
  }
}

after bumping the scala version 2.12.3 to 2.12.4

i encountered this problem with my scala implementation of https://github.com/square/retrofit/blob/master/retrofit/src/main/java/retrofit2/Converter.java

access to getParameterUpperBound, getRawType stopped working