bugfix: Don't use cache directory with null in it's path

This is a bug in ProjectDirectories, which seems to be super hard to fix, so instead we can special case it. This is not super important to use that directory anyway, we fall back to local workspace.

Fixes scalameta#5590

Author: tgodzik

metals/src/main/scala/scala/meta/internal/metals/Trace.scala

@@ -26,8 +26,13 @@ object Trace {
       // the path making it difficult to tail/cat from the terminal and cmd+click from VS Code.
       // Instead, we use the `cacheDir` which has no spaces. The logs are safe to remove so
       // putting them in the "cache directory" makes more sense compared to the "config directory".
-      AbsolutePath(projectDirectories.cacheDir)
-    }.toOption
+      val cacheDir = projectDirectories.cacheDir
+      // https://github.com/scalameta/metals/issues/5590
+      // deal with issue on windows and PowerShell, which would cause us to create a null directory in the workspace
+      if (cacheDir.startsWith("null\\"))
+        None
+      else Some(AbsolutePath(cacheDir))
+    }.toOption.flatten
 
   private val localDirectory: AbsolutePath =
     PathIO.workingDirectory.resolve(".metals/")