8254876: (fs) NullPointerException not thrown when first argument to Path.of or Paths.get is null

Reviewed-by: rriggs, alanb

src/java.base/unix/classes/sun/nio/fs/UnixFileSystem.java

@@ -257,6 +257,7 @@ abstract class UnixFileSystem
 
     @Override
     public final Path getPath(String first, String... more) {
+        Objects.requireNonNull(first);
         String path;
         if (more.length == 0) {
             path = first;