[GR-58237] Improve the error message when NativeImageFileSystemProvider is not present.

PullRequest: graal/18955

Author: jovanstevanovic

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/resources/NativeImageResourceFileSystemProvider.java

@@ -25,8 +25,6 @@
 
 package com.oracle.svm.core.jdk.resources;
 
-import com.oracle.svm.core.jdk.JavaNetSubstitutions;
-
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -56,6 +54,8 @@
 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 
+import com.oracle.svm.core.jdk.JavaNetSubstitutions;
+
 public class NativeImageResourceFileSystemProvider extends FileSystemProvider {
 
     private final String resourcePath = "/resources";
@@ -141,7 +141,8 @@ public FileSystem getFileSystem(URI uri) {
         try {
             readLock.lock();
             if (fileSystem == null) {
-                throw new FileSystemNotFoundException();
+                throw new FileSystemNotFoundException("The Native Image Resource File System is not present. " +
+                                "Please create a new file system using the `newFileSystem` operation before attempting any file system operations on resource URIs.");
             }
             return fileSystem;
         } finally {