deal with unsafe nulls and fix sorting

[Cherry-picked 637b1d3]

Author: kasiaMarek

presentation-compiler/src/main/dotty/tools/pc/completions/Completions.scala

@@ -926,6 +926,7 @@ class Completions(
           v match
             case _: CompletionValue.SingletonValue => 0
             case _: CompletionValue.Compiler => 1
+            case CompletionValue.ExtraMethod(_, _: CompletionValue.Compiler) => 1
             case _: CompletionValue.CaseKeyword => 2
             case _: CompletionValue.NamedArg => 3
             case _: CompletionValue.Keyword => 4

presentation-compiler/src/main/dotty/tools/pc/completions/SingletonCompletions.scala

@@ -32,7 +32,7 @@ object SingletonCompletions:
           case (i @ Ident(name)) :: _ => List(name.toString() -> i.span)
           case (l @ Literal(const)) :: _ => List(const.show -> l.span)
           case _ => Nil
-      query = name.replace(Cursor.value, "")
+      query = name.replace(Cursor.value, "").nn
       tpe = tpe0 match
         // for Tuple 2 we want to suggest first arg completion
         case AppliedType(t: TypeRef, args) if t.classSymbol == Symbols.defn.Tuple2 && args.nonEmpty =>

presentation-compiler/test/dotty/tools/pc/tests/PcReferencesSuite.scala

@@ -1,12 +1,16 @@
 package dotty.tools.pc.tests
+
+import scala.language.unsafeNulls
+
 import dotty.tools.pc.base.BasePCSuite
 import dotty.tools.pc.utils.RangeReplace
-import scala.meta.internal.pc.PcReferencesRequest
-import scala.meta.internal.metals.CompilerVirtualFileParams
+
 import java.net.URI
-import scala.meta.internal.metals.EmptyCancelToken
 import org.eclipse.lsp4j.jsonrpc.messages.{Either => JEither}
 import scala.meta.internal.jdk.CollectionConverters.*
+import scala.meta.internal.metals.CompilerVirtualFileParams
+import scala.meta.internal.metals.EmptyCancelToken
+import scala.meta.internal.pc.PcReferencesRequest
 
 import org.junit.Test