diff --git a/compiler/src/dotty/tools/backend/jvm/ClassfileWriters.scala b/compiler/src/dotty/tools/backend/jvm/ClassfileWriters.scala
index e2730c1e84ab..e2ce73f79028 100644
--- a/compiler/src/dotty/tools/backend/jvm/ClassfileWriters.scala
+++ b/compiler/src/dotty/tools/backend/jvm/ClassfileWriters.scala
@@ -18,8 +18,6 @@ import BTypes.InternalName
 import scala.util.chaining.*
 import dotty.tools.io.JarArchive
 
-import scala.language.unsafeNulls
-
 /** !!! This file is now copied in `dotty.tools.io.FileWriters` in a more general way that does not rely upon
  * `PostProcessorFrontendAccess`, this should probably be changed to wrap that class instead.
  *
@@ -54,11 +52,11 @@ class ClassfileWriters(frontendAccess: PostProcessorFrontendAccess) {
     def close(): Unit
 
     protected def classRelativePath(className: InternalName, suffix: String = ".class"): String =
-      className.replace('.', '/').nn + suffix
+      className.replace('.', '/') + suffix
   }
 
   object ClassfileWriter {
-    private def getDirectory(dir: String): Path = Paths.get(dir).nn
+    private def getDirectory(dir: String): Path = Paths.get(dir)
 
     def apply(): ClassfileWriter = {
       val jarManifestMainClass: Option[String] = compilerSettings.mainClass.orElse {
@@ -137,7 +135,7 @@ class ClassfileWriters(frontendAccess: PostProcessorFrontendAccess) {
         new JarEntryWriter(jarFile, jarManifestMainClass, jarCompressionLevel)
       }
       else if (file.isVirtual) new VirtualFileWriter(file)
-      else if (file.isDirectory) new DirEntryWriter(file.file.toPath.nn)
+      else if (file.isDirectory) new DirEntryWriter(file.file.toPath)
       else throw new IllegalStateException(s"don't know how to handle an output of $file [${file.getClass}]")
   }
 
@@ -151,7 +149,7 @@ class ClassfileWriters(frontendAccess: PostProcessorFrontendAccess) {
     val jarWriter: JarOutputStream = {
       import scala.util.Properties.*
       val manifest = new Manifest
-      val attrs = manifest.getMainAttributes.nn
+      val attrs = manifest.getMainAttributes
       attrs.put(MANIFEST_VERSION, "1.0")
       attrs.put(ScalaCompilerVersion, versionNumberString)
       mainClass.foreach(c => attrs.put(MAIN_CLASS, c))
@@ -184,7 +182,7 @@ class ClassfileWriters(frontendAccess: PostProcessorFrontendAccess) {
       // important detail here, even on Windows, Zinc expects the separator within the jar
       // to be the system default, (even if in the actual jar file the entry always uses '/').
       // see https://github.com/sbt/zinc/blob/dcddc1f9cfe542d738582c43f4840e17c053ce81/internal/compiler-bridge/src/main/scala/xsbt/JarUtils.scala#L47
-      val pathInJar = 
+      val pathInJar =
         if File.separatorChar == '/' then relativePath
         else relativePath.replace('/', File.separatorChar)
       PlainFile.toPlainFile(Paths.get(s"${file.absolutePath}!$pathInJar"))
@@ -293,5 +291,5 @@ class ClassfileWriters(frontendAccess: PostProcessorFrontendAccess) {
   }
 
   /** Can't output a file due to the state of the file system. */
-  class FileConflictException(msg: String, cause: Throwable = null) extends IOException(msg, cause)
+  class FileConflictException(msg: String, cause: Throwable | Null = null) extends IOException(msg, cause)
 }
diff --git a/compiler/src/dotty/tools/dotc/Driver.scala b/compiler/src/dotty/tools/dotc/Driver.scala
index 98abe2ac6c38..a401bb689db0 100644
--- a/compiler/src/dotty/tools/dotc/Driver.scala
+++ b/compiler/src/dotty/tools/dotc/Driver.scala
@@ -38,7 +38,7 @@ class Driver {
         finish(compiler, run)
       catch
         case ex: FatalError =>
-          report.error(ex.getMessage.nn) // signals that we should fail compilation.
+          report.error(ex.getMessage) // signals that we should fail compilation.
         case ex: Throwable if ctx.usedBestEffortTasty =>
           report.bestEffortError(ex, "Some best-effort tasty files were not able to be read.")
           throw ex
@@ -117,7 +117,7 @@ class Driver {
         .distinct
       val ctx1 = ctx.fresh
       val fullClassPath =
-        (newEntries :+ ctx.settings.classpath.value).mkString(java.io.File.pathSeparator.nn)
+        (newEntries :+ ctx.settings.classpath.value).mkString(java.io.File.pathSeparator)
       ctx1.setSetting(ctx1.settings.classpath, fullClassPath)
     else ctx
 
diff --git a/compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala b/compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala
index ec134149eb49..500765b04980 100644
--- a/compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala
+++ b/compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala
@@ -963,7 +963,7 @@ class CheckCaptures extends Recheck, SymTransformer:
             trace.force(i"rechecking $tree with pt = $pt", recheckr, show = true):
               super.recheck(tree, pt)
         catch case ex: NoCommonRoot =>
-          report.error(ex.getMessage.nn)
+          report.error(ex.getMessage)
           tree.tpe
         finally curEnv = saved
       if tree.isTerm then
diff --git a/compiler/src/dotty/tools/dotc/classpath/ClassPathFactory.scala b/compiler/src/dotty/tools/dotc/classpath/ClassPathFactory.scala
index 080f8d4e63d2..416bcc85a783 100644
--- a/compiler/src/dotty/tools/dotc/classpath/ClassPathFactory.scala
+++ b/compiler/src/dotty/tools/dotc/classpath/ClassPathFactory.scala
@@ -67,7 +67,7 @@ class ClassPathFactory {
         for
           file <- files
           a <- ClassPath.expandManifestPath(file.absolutePath)
-          path = java.nio.file.Paths.get(a.toURI()).nn
+          path = java.nio.file.Paths.get(a.toURI())
           if Files.exists(path)
         yield
           newClassPath(AbstractFile.getFile(path))
diff --git a/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala b/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala
index 855c0410042a..50aa89779f50 100644
--- a/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala
+++ b/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala
@@ -118,8 +118,8 @@ object CommandLineParser:
       Nil
     else
       def stripComment(s: String) = s.indexOf('#') match { case -1 => s case i => s.substring(0, i) }
-      val lines = Files.readAllLines(path).nn
-      val params = lines.asScala.map(stripComment).filter(!_.nn.isEmpty).mkString(" ")
+      val lines = Files.readAllLines(path)
+      val params = lines.asScala.map(stripComment).filter(!_.isEmpty).mkString(" ")
       tokenize(params)
 
   class ParseException(msg: String) extends RuntimeException(msg)
diff --git a/compiler/src/dotty/tools/dotc/core/Comments.scala b/compiler/src/dotty/tools/dotc/core/Comments.scala
index 92160c97973d..5ee1d5856605 100644
--- a/compiler/src/dotty/tools/dotc/core/Comments.scala
+++ b/compiler/src/dotty/tools/dotc/core/Comments.scala
@@ -2,8 +2,6 @@ package dotty.tools
 package dotc
 package core
 
-import scala.language.unsafeNulls
-
 import ast.{ untpd, tpd }
 import Symbols.*, Contexts.*
 import util.{SourceFile, ReadOnlyMap}
diff --git a/compiler/src/dotty/tools/dotc/core/Decorators.scala b/compiler/src/dotty/tools/dotc/core/Decorators.scala
index 29d4b3fa4052..765fbd2907fc 100644
--- a/compiler/src/dotty/tools/dotc/core/Decorators.scala
+++ b/compiler/src/dotty/tools/dotc/core/Decorators.scala
@@ -51,7 +51,7 @@ object Decorators {
         if name.length != 0 then name.getChars(0, name.length, chars, s.length)
         termName(chars, 0, len)
       case name: TypeName => s.concat(name.toTermName)
-      case _ => termName(s.concat(name.toString).nn)
+      case _ => termName(s.concat(name.toString))
 
     def indented(width: Int): String =
       val padding = " " * width
@@ -289,10 +289,10 @@ object Decorators {
           case NonFatal(ex)
           if !ctx.settings.YshowPrintErrors.value =>
             s"... (cannot display due to ${ex.className} ${ex.getMessage}) ..."
-      case _ => String.valueOf(x).nn
+      case _ => String.valueOf(x)
 
     /** Returns the simple class name of `x`. */
-    def className: String = x.getClass.getSimpleName.nn
+    def className: String = x.getClass.getSimpleName
 
   extension [T](x: T)
     def assertingErrorsReported(using Context): T = {
diff --git a/compiler/src/dotty/tools/dotc/core/NameOps.scala b/compiler/src/dotty/tools/dotc/core/NameOps.scala
index 544718508e9e..ce726785e7e7 100644
--- a/compiler/src/dotty/tools/dotc/core/NameOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/NameOps.scala
@@ -15,7 +15,7 @@ import nme.*
 object NameOps {
 
   object compactify {
-    lazy val md5: MessageDigest = MessageDigest.getInstance("MD5").nn
+    lazy val md5: MessageDigest = MessageDigest.getInstance("MD5")
 
     inline val CLASSFILE_NAME_CHAR_LIMIT = 240
 
@@ -43,7 +43,7 @@ object NameOps {
         val suffix = s.takeRight(edge)
 
         val cs = s.toArray
-        val bytes = Codec.toUTF8(CharBuffer.wrap(cs).nn)
+        val bytes = Codec.toUTF8(CharBuffer.wrap(cs))
         md5.update(bytes)
         val md5chars = md5.digest().map(b => (b & 0xFF).toHexString).mkString
 
diff --git a/compiler/src/dotty/tools/dotc/core/TypeErrors.scala b/compiler/src/dotty/tools/dotc/core/TypeErrors.scala
index a65c0ada0c24..ce14cad6871c 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeErrors.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeErrors.scala
@@ -32,7 +32,7 @@ abstract class TypeError(using creationContext: Context) extends Exception(""):
     || ctx.settings.YdebugCyclic.value
 
   override def fillInStackTrace(): Throwable =
-    if computeStackTrace then super.fillInStackTrace().nn
+    if computeStackTrace then super.fillInStackTrace()
     else this
 
   /** Convert to message. This takes an additional Context, so that we
diff --git a/compiler/src/dotty/tools/dotc/core/TypeEval.scala b/compiler/src/dotty/tools/dotc/core/TypeEval.scala
index 4d5496cff880..a6c308bb2a55 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeEval.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeEval.scala
@@ -94,7 +94,7 @@ object TypeEval:
         val result =
           try op
           catch case e: Throwable =>
-            throw TypeError(em"${e.getMessage.nn}")
+            throw TypeError(em"${e.getMessage}")
         ConstantType(Constant(result))
 
       def fieldsOf: Option[Type] =
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/AttributeUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/AttributeUnpickler.scala
index 43a2bea27216..c5770d69b002 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/AttributeUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/AttributeUnpickler.scala
@@ -1,7 +1,6 @@
 package dotty.tools.dotc
 package core.tasty
 
-import scala.language.unsafeNulls
 import scala.collection.immutable.BitSet
 import scala.collection.immutable.TreeMap
 
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyPrinter.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyPrinter.scala
index 72f6895f122c..ee798e29721e 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TastyPrinter.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyPrinter.scala
@@ -53,7 +53,7 @@ object TastyPrinter:
       else if arg.endsWith(".tasty") || (allowBetasty && arg.endsWith(".betasty")) then
         val path = Paths.get(arg)
         if Files.exists(path) then
-          printTasty(arg, Files.readAllBytes(path).nn, arg.endsWith(".betasty"))
+          printTasty(arg, Files.readAllBytes(path), arg.endsWith(".betasty"))
         else
           println("File not found: " + arg)
           System.exit(1)
diff --git a/compiler/src/dotty/tools/dotc/plugins/Plugins.scala b/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
index a6672d475129..490d1683b304 100644
--- a/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
+++ b/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
@@ -1,8 +1,6 @@
 package dotty.tools.dotc
 package plugins
 
-import scala.language.unsafeNulls
-
 import core.*
 import Contexts.*
 import Decorators.em
@@ -47,13 +45,12 @@ trait Plugins {
     goods map (_.get)
   }
 
-  private var _roughPluginsList: List[Plugin] = uninitialized
+  private var _roughPluginsList: List[Plugin] | Null = null
   protected def roughPluginsList(using Context): List[Plugin] =
     if (_roughPluginsList == null) {
       _roughPluginsList = loadRoughPluginsList
-      _roughPluginsList
     }
-    else _roughPluginsList
+    _roughPluginsList.nn
 
   /** Load all available plugins. Skips plugins that
    *  either have the same name as another one, or which
@@ -99,13 +96,12 @@ trait Plugins {
     plugs
   }
 
-  private var _plugins: List[Plugin] = uninitialized
+  private var _plugins: List[Plugin] | Null = null
   def plugins(using Context): List[Plugin] =
     if (_plugins == null) {
       _plugins = loadPlugins
-      _plugins
     }
-    else _plugins
+    _plugins.nn
 
   /** A description of all the plugins that are loaded */
   def pluginDescriptions(using Context): String =
diff --git a/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala b/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
index b5ed3bdb4fa7..00b22f2b7df3 100644
--- a/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
+++ b/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
@@ -394,7 +394,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
       case tp: ThisType =>
         nameString(tp.cls) + ".this"
       case SuperType(thistpe: SingletonType, _) =>
-        toTextRef(thistpe).map(_.replaceAll("""\bthis$""", "super").nn)
+        toTextRef(thistpe).map(_.replaceAll("""\bthis$""", "super"))
       case SuperType(thistpe, _) =>
         "Super(" ~ toTextGlobal(thistpe) ~ ")"
       case tp @ ConstantType(value) =>
@@ -628,7 +628,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
     case '"' => "\\\""
     case '\'' => "\\\'"
     case '\\' => "\\\\"
-    case _ => if ch.isControl then f"${"\\"}u${ch.toInt}%04x" else String.valueOf(ch).nn
+    case _ => if ch.isControl then f"${"\\"}u${ch.toInt}%04x" else String.valueOf(ch)
   }
 
   def toText(const: Constant): Text = const.tag match {
@@ -638,7 +638,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
     case LongTag => literalText(const.longValue.toString + "L")
     case DoubleTag => literalText(const.doubleValue.toString + "d")
     case FloatTag => literalText(const.floatValue.toString + "f")
-    case _ => literalText(String.valueOf(const.value).nn)
+    case _ => literalText(String.valueOf(const.value))
   }
 
   /** Usual target for `Annotation#toText`, overridden in RefinedPrinter */
diff --git a/compiler/src/dotty/tools/dotc/printing/Showable.scala b/compiler/src/dotty/tools/dotc/printing/Showable.scala
index 4480aa9c76a4..490778a7413a 100644
--- a/compiler/src/dotty/tools/dotc/printing/Showable.scala
+++ b/compiler/src/dotty/tools/dotc/printing/Showable.scala
@@ -25,7 +25,7 @@ trait Showable extends Any {
   /** The string representation with each line after the first one indented
    *  by the given given margin (in spaces).
    */
-  def showIndented(margin: Int)(using Context): String = show.replace("\n", "\n" + " " * margin).nn
+  def showIndented(margin: Int)(using Context): String = show.replace("\n", "\n" + " " * margin)
 
   /** The summarized string representation of this showable element.
    *  Recursion depth is limited to some smallish value. Default is
diff --git a/compiler/src/dotty/tools/dotc/printing/Texts.scala b/compiler/src/dotty/tools/dotc/printing/Texts.scala
index 4db0c83fed58..014765b63274 100644
--- a/compiler/src/dotty/tools/dotc/printing/Texts.scala
+++ b/compiler/src/dotty/tools/dotc/printing/Texts.scala
@@ -5,7 +5,7 @@ import scala.annotation.internal.sharable
 object Texts {
 
   @sharable
-  private val ansi = java.util.regex.Pattern.compile("\u001b\\[\\d+m").nn
+  private val ansi = java.util.regex.Pattern.compile("\u001b\\[\\d+m")
 
   sealed abstract class Text {
 
diff --git a/compiler/src/dotty/tools/dotc/quoted/Interpreter.scala b/compiler/src/dotty/tools/dotc/quoted/Interpreter.scala
index e34d35065476..dbc2694dc891 100644
--- a/compiler/src/dotty/tools/dotc/quoted/Interpreter.scala
+++ b/compiler/src/dotty/tools/dotc/quoted/Interpreter.scala
@@ -1,8 +1,6 @@
 package dotty.tools.dotc
 package quoted
 
-import scala.language.unsafeNulls
-
 import scala.collection.mutable
 import scala.reflect.ClassTag
 
diff --git a/compiler/src/dotty/tools/dotc/reporting/messages.scala b/compiler/src/dotty/tools/dotc/reporting/messages.scala
index 01eb2acfa4de..396f2eadc332 100644
--- a/compiler/src/dotty/tools/dotc/reporting/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/messages.scala
@@ -92,7 +92,7 @@ abstract class CyclicMsg(errorId: ErrorMessageID)(using Context) extends Message
 
   protected def debugInfo =
     if ctx.settings.YdebugCyclic.value then
-      "\n\nStacktrace:" ++ ex.getStackTrace().nn.mkString("\n    ", "\n    ", "")
+      "\n\nStacktrace:" ++ ex.getStackTrace().mkString("\n    ", "\n    ", "")
     else "\n\n Run with both -explain-cyclic and -Ydebug-cyclic to see full stack trace."
 
   protected def context: String = ex.optTrace match
diff --git a/compiler/src/dotty/tools/dotc/semanticdb/Scala3.scala b/compiler/src/dotty/tools/dotc/semanticdb/Scala3.scala
index f49b00089712..a20a0d181a55 100644
--- a/compiler/src/dotty/tools/dotc/semanticdb/Scala3.scala
+++ b/compiler/src/dotty/tools/dotc/semanticdb/Scala3.scala
@@ -420,7 +420,7 @@ object Scala3:
         else Descriptor.None
 
       def unescapeUnicode =
-        unicodeEscape.replaceAllIn(symbol, m => String.valueOf(Integer.parseInt(m.group(1), 16).toChar).nn)
+        unicodeEscape.replaceAllIn(symbol, m => String.valueOf(Integer.parseInt(m.group(1), 16).toChar))
 
       def isJavaIdent =
         symbol.nonEmpty && isJavaIdentifierStart(symbol.head) && symbol.tail.forall(isJavaIdentifierPart)
diff --git a/compiler/src/dotty/tools/dotc/transform/Pickler.scala b/compiler/src/dotty/tools/dotc/transform/Pickler.scala
index c8c071064ab8..108277599010 100644
--- a/compiler/src/dotty/tools/dotc/transform/Pickler.scala
+++ b/compiler/src/dotty/tools/dotc/transform/Pickler.scala
@@ -258,7 +258,7 @@ class Pickler extends Phase {
   }
 
   private def computeInternalName(cls: ClassSymbol)(using Context): String =
-    if cls.is(Module) then cls.binaryClassName.stripSuffix(str.MODULE_SUFFIX).nn
+    if cls.is(Module) then cls.binaryClassName.stripSuffix(str.MODULE_SUFFIX)
     else cls.binaryClassName
 
   override def run(using Context): Unit = {
@@ -413,11 +413,11 @@ class Pickler extends Phase {
       )
     if ctx.isBestEffort then
       val outpath =
-        ctx.settings.outputDir.value.jpath.toAbsolutePath.nn.normalize.nn
-          .resolve("META-INF").nn
+        ctx.settings.outputDir.value.jpath.toAbsolutePath.normalize
+          .resolve("META-INF")
           .resolve("best-effort")
       Files.createDirectories(outpath)
-      BestEffortTastyWriter.write(outpath.nn, result)
+      BestEffortTastyWriter.write(outpath, result)
     result
   }
 
diff --git a/compiler/src/dotty/tools/dotc/transform/init/Errors.scala b/compiler/src/dotty/tools/dotc/transform/init/Errors.scala
index 85feb609c90a..0b843b4b33fd 100644
--- a/compiler/src/dotty/tools/dotc/transform/init/Errors.scala
+++ b/compiler/src/dotty/tools/dotc/transform/init/Errors.scala
@@ -31,7 +31,7 @@ object Errors:
       report.warning(show, this.pos)
   end Error
 
-  override def toString() = this.getClass.getName.nn
+  override def toString() = this.getClass.getName
 
   /** Access non-initialized field */
   case class AccessNonInit(field: Symbol)(val trace: Trace) extends Error:
diff --git a/compiler/src/dotty/tools/dotc/transform/init/Trace.scala b/compiler/src/dotty/tools/dotc/transform/init/Trace.scala
index ffaccad963af..9a00589197d5 100644
--- a/compiler/src/dotty/tools/dotc/transform/init/Trace.scala
+++ b/compiler/src/dotty/tools/dotc/transform/init/Trace.scala
@@ -51,7 +51,7 @@ object Trace:
       val line =
         if pos.source.exists then
           val loc = "[ " + pos.source.file.name + ":" + (pos.line + 1) + " ]"
-          val code = SyntaxHighlighting.highlight(pos.lineContent.trim.nn)
+          val code = SyntaxHighlighting.highlight(pos.lineContent.trim)
           i"$code\t$loc"
         else
           tree match
@@ -59,7 +59,7 @@ object Trace:
               // The definition can be huge, avoid printing the whole definition.
               defDef.symbol.showFullName
             case _ =>
-              tree.show.split(System.lineSeparator(), 2).nn.head.nn
+              tree.show.split(System.lineSeparator(), 2).head
 
       val positionMarkerLine =
         if pos.exists && pos.source.exists then
@@ -86,7 +86,7 @@ object Trace:
    */
   private def positionMarker(pos: SourcePosition): String =
     val trimmed = pos.source.lineContent(pos.start).takeWhile(c => c.isWhitespace).length
-    val padding = pos.startColumnPadding.substring(trimmed).nn
+    val padding = pos.startColumnPadding.substring(trimmed)
     val carets =
       if (pos.startLine == pos.endLine)
         "^" * math.max(1, pos.endColumn - pos.startColumn)
diff --git a/compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala b/compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala
index 9e40792895c0..5ac96f58011b 100644
--- a/compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala
+++ b/compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala
@@ -74,7 +74,7 @@ class TypedFormatChecker(partsElems: List[Tree], parts: List[String], args: List
     def loop(remaining: List[String], n: Int): Unit =
       remaining match
         case part0 :: more =>
-          def badPart(t: Throwable): String = "".tap(_ => report.partError(t.getMessage.nn, index = n, offset = 0))
+          def badPart(t: Throwable): String = "".tap(_ => report.partError(t.getMessage, index = n, offset = 0))
           val part = try StringContext.processEscapes(part0) catch badPart
           val matches = formatPattern.findAllMatchIn(part)
 
diff --git a/compiler/src/dotty/tools/dotc/transform/sjs/PrepJSInterop.scala b/compiler/src/dotty/tools/dotc/transform/sjs/PrepJSInterop.scala
index 1b8fdd268ece..595a2e9a70ad 100644
--- a/compiler/src/dotty/tools/dotc/transform/sjs/PrepJSInterop.scala
+++ b/compiler/src/dotty/tools/dotc/transform/sjs/PrepJSInterop.scala
@@ -651,7 +651,7 @@ class PrepJSInterop extends MacroTransform with IdentityDenotTransformer { thisP
           val dotIndex = pathName.indexOf('.')
           val globalRef =
             if (dotIndex < 0) pathName
-            else pathName.substring(0, dotIndex).nn
+            else pathName.substring(0, dotIndex)
           checkGlobalRefName(globalRef)
         }
 
diff --git a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
index 0a0356707048..c9cd2b05a94a 100644
--- a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -1259,9 +1259,9 @@ object RefChecks {
       val matches = referencePattern.findAllIn(s)
       for reference <- matches do
         val referenceOffset = matches.start
-        val prefixlessReference = reference.replaceFirst("""\$\{\s*""", "").nn
+        val prefixlessReference = reference.replaceFirst("""\$\{\s*""", "")
         val variableOffset = referenceOffset + reference.length - prefixlessReference.length
-        val variableName = prefixlessReference.replaceFirst("""\s*\}""", "").nn
+        val variableName = prefixlessReference.replaceFirst("""\s*\}""", "")
         f(variableName, variableOffset)
 
   end checkImplicitNotFoundAnnotation
diff --git a/compiler/src/dotty/tools/dotc/util/ShowPickled.scala b/compiler/src/dotty/tools/dotc/util/ShowPickled.scala
index 8d5d0c27ab0e..15d553e703b3 100644
--- a/compiler/src/dotty/tools/dotc/util/ShowPickled.scala
+++ b/compiler/src/dotty/tools/dotc/util/ShowPickled.scala
@@ -113,7 +113,7 @@ object ShowPickled {
     result.toInt
   }
 
-  def printFile(buf: PickleBuffer, out: PrintStream = System.out.nn): Unit = {
+  def printFile(buf: PickleBuffer, out: PrintStream = System.out): Unit = {
     out.println("Version " + buf.readNat() + "." + buf.readNat())
     val index = buf.createIndex
     val entryList = makeEntryList(buf, index)
diff --git a/compiler/src/dotty/tools/io/FileWriters.scala b/compiler/src/dotty/tools/io/FileWriters.scala
index 38bca796373e..849b80c5e745 100644
--- a/compiler/src/dotty/tools/io/FileWriters.scala
+++ b/compiler/src/dotty/tools/io/FileWriters.scala
@@ -189,7 +189,7 @@ object FileWriters {
     def close(): Unit
 
     protected def classToRelativePath(className: InternalName): String =
-      className.replace('.', '/').nn + ".tasty"
+      className.replace('.', '/') + ".tasty"
   }
 
   object TastyWriter {
@@ -234,7 +234,7 @@ object FileWriters {
         new JarEntryWriter(jarFile, jarManifestMainClass, jarCompressionLevel)
       }
       else if (file.isVirtual) new VirtualFileWriter(file)
-      else if (file.isDirectory) new DirEntryWriter(file.file.toPath.nn)
+      else if (file.isDirectory) new DirEntryWriter(file.file.toPath)
       else throw new IllegalStateException(s"don't know how to handle an output of $file [${file.getClass}]")
   }
 
@@ -248,7 +248,7 @@ object FileWriters {
     val jarWriter: JarOutputStream = {
       import scala.util.Properties.*
       val manifest = new Manifest
-      val attrs = manifest.getMainAttributes.nn
+      val attrs = manifest.getMainAttributes
       attrs.put(MANIFEST_VERSION, "1.0")
       attrs.put(ScalaCompilerVersion, versionNumberString)
       mainClass.foreach(c => attrs.put(MAIN_CLASS, c))
diff --git a/compiler/src/dotty/tools/io/Path.scala b/compiler/src/dotty/tools/io/Path.scala
index 6f97e03ca4d7..39665395c289 100644
--- a/compiler/src/dotty/tools/io/Path.scala
+++ b/compiler/src/dotty/tools/io/Path.scala
@@ -5,8 +5,6 @@
 
 package dotty.tools.io
 
-import scala.language.unsafeNulls
-
 import java.io.RandomAccessFile
 import java.nio.file.*
 import java.net.{URI, URL}
@@ -46,7 +44,7 @@ object Path {
   def fileName(name: String): String = {
     val i = name.lastIndexOf('.')
     if (i < 0) name
-    else name.substring(0, i).nn
+    else name.substring(0, i)
   }
 
   def onlyDirs(xs: Iterator[Path]): Iterator[Directory] = xs.filter(_.isDirectory).map(_.toDirectory)
diff --git a/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala b/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala
index 9503177ff738..86ba6708caba 100644
--- a/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala
+++ b/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala
@@ -1441,7 +1441,7 @@ object SourceCode {
       case '"' => "\\\""
       case '\'' => "\\\'"
       case '\\' => "\\\\"
-      case _ => if ch.isControl then f"${"\\"}u${ch.toInt}%04x" else String.valueOf(ch).nn
+      case _ => if ch.isControl then f"${"\\"}u${ch.toInt}%04x" else String.valueOf(ch)
     }
 
     private def escapedString(str: String): String = str flatMap escapedChar
diff --git a/compiler/test/dotty/tools/backend/jvm/StringConcatTest.scala b/compiler/test/dotty/tools/backend/jvm/StringConcatTest.scala
index 14352106c5e8..613e72b32e52 100644
--- a/compiler/test/dotty/tools/backend/jvm/StringConcatTest.scala
+++ b/compiler/test/dotty/tools/backend/jvm/StringConcatTest.scala
@@ -122,7 +122,7 @@ class StringConcatTest extends DottyBytecodeTest {
            chsq: java.lang.CharSequence,
            chrs: Array[Char]) = {
       val s1 = str + obj + v + z + c + b + s + i + f + l + d + sbuf + chsq + chrs
-      val s2 = String.valueOf(obj).nn + str + v + z + c + b + s + i + f + l + d + sbuf + chsq + chrs
+      val s2 = String.valueOf(obj) + str + v + z + c + b + s + i + f + l + d + sbuf + chsq + chrs
       s1 + "//" + s2
     }
     def sbuf = { val r = new java.lang.StringBuffer(); r.append("sbuf"); r }
diff --git a/compiler/test/dotty/tools/dotc/SettingsTests.scala b/compiler/test/dotty/tools/dotc/SettingsTests.scala
index 996ab22f67b1..ec342db875a6 100644
--- a/compiler/test/dotty/tools/dotc/SettingsTests.scala
+++ b/compiler/test/dotty/tools/dotc/SettingsTests.scala
@@ -1,8 +1,6 @@
 package dotty.tools
 package dotc
 
-import scala.language.unsafeNulls
-
 import reporting.StoreReporter
 import vulpix.TestConfiguration
 
@@ -205,7 +203,7 @@ class SettingsTests {
     }
 
   @Test def `Output setting is overriding existing jar`: Unit =
-    val result = Using.resource(Files.createTempFile("myfile", ".jar").nn){ file =>
+    val result = Using.resource(Files.createTempFile("myfile", ".jar")){ file =>
       object Settings extends SettingGroup:
         val defaultDir = new PlainDirectory(Directory("."))
         val testOutput = OutputSetting(RootSetting, "testOutput", "testOutput", "", defaultDir)
@@ -224,7 +222,7 @@ class SettingsTests {
 
   @Test def `Output setting is respecting previous setting`: Unit =
     val result = Using.resources(
-      Files.createTempFile("myfile", ".jar").nn, Files.createTempFile("myfile2", ".jar").nn
+      Files.createTempFile("myfile", ".jar"), Files.createTempFile("myfile2", ".jar")
     ){ (file1, file2) =>
       object Settings extends SettingGroup:
         val defaultDir = new PlainDirectory(Directory("."))
@@ -250,7 +248,7 @@ class SettingsTests {
     }(Files.deleteIfExists(_), Files.deleteIfExists(_))
 
   @Test def `Output side effect is not present when setting is deprecated`: Unit =
-    val result = Using.resource(Files.createTempFile("myfile", ".jar").nn){ file =>
+    val result = Using.resource(Files.createTempFile("myfile", ".jar")){ file =>
       object Settings extends SettingGroup:
         val defaultDir = new PlainDirectory(Directory("."))
         val testOutput = OutputSetting(RootSetting, "testOutput", "testOutput", "", defaultDir, preferPrevious = true, deprecation = Deprecation.renamed("XtestOutput"))
diff --git a/compiler/test/dotty/tools/dotc/TupleShowTests.scala b/compiler/test/dotty/tools/dotc/TupleShowTests.scala
index 2d76c480b001..88e0587d7d71 100644
--- a/compiler/test/dotty/tools/dotc/TupleShowTests.scala
+++ b/compiler/test/dotty/tools/dotc/TupleShowTests.scala
@@ -71,7 +71,7 @@ class TupleShowTests extends DottyTest:
   /** On Windows the string literal in this test source file will be read with `\n` (b/c of "-encoding UTF8")
   *   but the compiler will correctly emit \r\n as the line separator.
   *   So we align the expected result to faithfully compare test results. */
-  extension (str: String) def normEOL = if EOL == "\n" then str else str.replace("\n", EOL).nn
+  extension (str: String) def normEOL = if EOL == "\n" then str else str.replace("\n", EOL)
 
   def diff(exp: String, obt: String) =
     val min = math.min(exp.length, obt.length)
diff --git a/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala b/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala
index bde4246ef0f0..ddc88803854f 100644
--- a/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala
+++ b/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala
@@ -265,7 +265,7 @@ class TastyHeaderUnpicklerTest {
 object TastyHeaderUnpicklerTest {
 
   def fillHeader(maj: Int, min: Int, exp: Int, compiler: String): TastyBuffer = {
-    val compilerBytes = compiler.getBytes(java.nio.charset.StandardCharsets.UTF_8).nn
+    val compilerBytes = compiler.getBytes(java.nio.charset.StandardCharsets.UTF_8)
     val buf = new TastyBuffer(header.length + 32 + compilerBytes.length)
     for (ch <- header) buf.writeByte(ch.toByte)
     buf.writeNat(maj)
@@ -304,7 +304,7 @@ object TastyHeaderUnpicklerTest {
       fail()
     }
     catch {
-      case err: UnpickleException => assert(err.getMessage.nn.contains(message))
+      case err: UnpickleException => assert(err.getMessage.contains(message))
     }
   }