Special case .toString for null and empty String

Author: OlivierBlanvillain

compiler/src/dotty/tools/repl/Rendering.scala

@@ -43,25 +43,29 @@ private[repl] class Rendering(compiler: ReplCompiler,
       myClassLoader
     }
 
-  /** Load the value of the symbol using reflection
+  /** Load the value of the symbol using reflection.
    *
    *  Calling this method evaluates the expression using reflection
    */
   private[this] def valueOf(sym: Symbol)(implicit ctx: Context): Option[String] = {
     val defn = ctx.definitions
-    val objectName = sym.owner.fullName.encode.toString.dropRight(1) // gotta drop the '$'
+    val objectName = sym.owner.fullName.encode.toString.stripSuffix("$")
     val resObj: Class[_] = Class.forName(objectName, true, classLoader())
-    val res =
+    val value =
       resObj
-        .getDeclaredMethods.find(_.getName == sym.name.toString).get
-        .invoke(null).toString
-
+        .getDeclaredMethods.find(_.getName == sym.name.encode.toString).get
+        .invoke(null)
+    val string = value match {
+      case null => "null" // Calling .toString on null => NPE
+      case ""   => "\"\"" // Sepcial cased for empty string, following scalac
+      case x    => x.toString
+    }
     if (!sym.is(Flags.Method) && sym.info == defn.UnitType)
       None
-    else if (res.startsWith(str.REPL_SESSION_LINE))
-      Some(res.drop(str.REPL_SESSION_LINE.length).dropWhile(c => c.isDigit || c == '$'))
+    else if (string.startsWith(str.REPL_SESSION_LINE))
+      Some(string.drop(str.REPL_SESSION_LINE.length).dropWhile(c => c.isDigit || c == '$'))
     else
-      Some(res)
+      Some(string)
   }
 
   /** Render method definition result */