src/Pure/PIDE/protocol_handlers.scala

--- a/src/Pure/PIDE/protocol_handlers.scala	Wed Apr 08 13:14:05 2020 +0200
+++ b/src/Pure/PIDE/protocol_handlers.scala	Wed Apr 08 14:06:26 2020 +0200
@@ -51,7 +51,10 @@
     def init(name: String): State =
     {
       val new_handler =
-        try { Some(Class.forName(name).newInstance.asInstanceOf[Session.Protocol_Handler]) }
+        try {
+          Some(Class.forName(name).getDeclaredConstructor().newInstance()
+            .asInstanceOf[Session.Protocol_Handler])
+        }
         catch { case exn: Throwable => bad_handler(exn, name); None }
       new_handler match { case Some(handler) => init(handler) case None => this }
     }